Alkaline battery and positive electrode material for alkaline battery

ABSTRACT

There is disclosed an alkaline battery including a positive electrode material mixture, a negative electrode, a separator interposed between the positive electrode material mixture and the negative electrode, and an alkaline electrolyte, wherein the positive electrode material mixture includes a first active material comprising nickel oxyhydroxide and a second active material comprising manganese dioxide, the nickel oxyhydroxide includes a γ-type crystal structure, the content of nickel in the nickel oxyhydroxide is not less than 45 wt %, and the average particle diameter on a volume basis of the nickel oxyhydroxide measured with a laser diffraction particle size distribution analyzer is 3 to 20 μm.

TECHNICAL FIELD

The present invention relates to an alkaline battery that comprises apositive electrode material mixture comprising nickel oxyhydroxide andmanganese dioxide, particularly to a nickel-manganese battery as aprimary battery. The present invention also relates to a method forproducing a positive electrode material for an alkaline batterycomprising nickel oxyhydroxide.

BACKGROUND ART

Alkaline batteries, in particular, discharge starting type alkalinebatteries or alkaline primary batteries have an inside-out typestructure in which a cylindrical positive electrode material mixturepellet is disposed in a positive electrode case serving as a positiveelectrode terminal such that the pellet is in close contact with thepositive electrode case, and a gelled zinc negative electrode isdisposed in a hollow portion of the pellet with a separator interposedtherebetween. With the recent widespread use of digital devices, theload power of the devices for which these batteries are used has beengradually increasing, and there has been a demand for batteries havingexcellent heavy load discharge characteristics. In response to such ademand, an alkaline battery whose heavy load discharge characteristicshave been improved by mixing nickel oxyhydroxide into a positiveelectrode material mixture has been proposed, and this has been recentlyput into practical use (Japanese Unexamined Patent Publication No. Sho57-72266).

On the other hand, in the field of alkaline storage batteries (secondarybatteries), nickel oxyhydroxide that is obtained by oxidizing sphericalor oval nickel hydroxide with an oxidizing agent such as a sodiumhypochlorite aqueous solution is generally used. As the source materialnickel hydroxide, nickel hydroxide having a high bulk density (tapdensity) and a β-type crystal structure are used. Nickel oxyhydroxidethat is obtained by treating this with an oxidizing agent mainly has aβ-type crystal structure, and can easily be filled at a high densityinside a battery. The nickel oxyhydroxide having a β-type crystalstructure has a nickel valence that is substantially 3, and theelectrochemical energy generated when this changes to a valence near 2is utilized as the discharge capacity of a battery.

For the purpose of increasing, for example, the utilization of thepositive electrode and the heavy load discharge characteristics, therehas also been proposed a technique that uses a solid solution nickelhydroxide in which cobalt, zinc or the like is dissolved, as thestarting material (Japanese Examined Patent Publication No. Hei7-77129).

Examples of the challenges that alkaline primary batteries containingnickel oxyhydroxide face are as follows:

(a) Improvement for the self decomposition (the decrease in the capacityand the increase in the internal pressure of the batteries) of nickeloxyhydroxide that occurs during storage of the batteries under a hightemperature atmosphere.

(b) Improvement for the low discharge capacity (discharge duration) dueto the small capacity per unit weight (mAh/g) of nickel oxyhydroxide.

In order to solve the above-described challenges, the followingproposals have been made for the positive electrode material mixture ofalkaline primary batteries.

First, from the viewpoint of improving the storage characteristics, ithas been proposed to contain, in nickel oxyhydroxide, at least one oxideselected from the group consisting of a zinc oxide, a calcium oxide, anyttrium oxide and titanium dioxide (Japanese Unexamined PatentPublication No. 2001-15106).

Further, in the alkaline storage battery applications, it has beenproposed to use a solid solution nickel hydroxide having a β-typecrystal structure and including a transition metal such as manganesedissolved in its particles, as the starting material (InternationalPublication No. WO 97/19479 and the specification of Japanese Patent No.3239076). Here, nickel oxyhydroxide having a γ-type crystal structureand an average valence of nickel near 3.5 was intentionally formedduring the charge reaction, thereby increasing the capacitysignificantly.

As a technique similar to this, for example, Japanese Unexamined PatentPublication No. 2001-322817 has proposed the use of particles of anα-type solid solution nickel hydroxide that was produced bycoprecipitating ions of a transition metal such as manganese or ironthat are in trivalent state with divalent nickel ions, as the startingmaterial. Here, nickel oxyhydroxide having a γ-type crystal structure isformed during charge, thus increasing the capacity.

Further, it has been proposed to improve the discharge characteristicsby coating the surface of particles of nickel oxyhydroxide having aγ-type crystal structure with a cobalt oxide having a high electricalconductivity (Japanese Unexamined Patent Publication Nos. Hei 10-334913and Hei 11-260364).

However, any attempt to increase the capacity by using nickeloxyhydroxide having a γ-type crystal structure for the positiveelectrode has not yet been put to practical use for alkaline storagebatteries. The reason lies in that a γ-type crystal excessively absorbsan electrolyte and thus expands in volume, so that the electrolytedistribution in the batteries greatly changes during the first severaltens of charge/discharge cycles. When the electrolyte is localized onthe positive electrode side and thus the electrolyte becomesinsufficient in the separator, the internal resistance in the batterysignificantly increases.

On the other hand, the present inventors attempted to use, for primarybatteries, nickel oxyhydroxide having a γ-type crystal structure, whichhas been investigated for alkaline storage batteries, and investigatedthe problems that could occur in such a case.

First, in the case of increasing the energy density of an alkalineprimary battery containing nickel oxyhydroxide, one possible approach isto set strong chemical oxidation conditions for a source material nickelhydroxide having a β-type crystal structure, thereby increasing thenickel valence of the resulting nickel oxyhydroxide having a β-typecrystal structure. Such an approach, however, can only provide nickeloxyhydroxide having a β-type crystal structure and in which the upperlimit of the nickel valence is less than 3.00 to 3.05.

Then, it was found that the heavy load discharge characteristics tendedto decrease more easily in the case of alkaline batteries as primarybatteries that used nickel oxyhydroxide having a γ-type crystalstructure, than in the case of alkaline batteries that used nickeloxyhydroxide having a β-type crystal structure, for the reasons shown in(a) to (c) below.

(a) The redox potential (equilibrium potential) of nickel oxyhydroxidehaving a γ-type crystal structure is lower than that of nickeloxyhydroxide having a β-type crystal structure.

(b) Nickel oxyhydroxide having a γ-type crystal structure undergoes alarge volume change (change in the crystal structure) that is causedduring discharge.

(c) The electron conductivity of nickel oxyhydroxide having a γ-typecrystal structure and including manganese dissolved in its particlesgreatly decreases with discharge.

For primary batteries such as nickel-manganese batteries, nickeloxyhydroxide is added to the positive electrode material mixture, inorder to compensate for the disadvantage of a low utilization ofmanganese dioxide during heavy load discharge. However, theabove-described finding means that a γ-type crystal structure maysignificantly impair the advantage that nickel oxyhydroxide improves theheavy load discharge characteristics of alkaline batteries.

DISCLOSURE OF INVENTION

The present invention solves or reduces the above-described problems byoptimizing the physical properties of nickel oxyhydroxide, therebymaking it possible to increase the capacity of, and to improve the heavyload discharge characteristics of alkaline batteries, in particularnickel-manganese batteries.

The present invention also solves or reduces the above-describedproblems by adding a specific element to nickel oxyhydroxide, therebymaking it possible to increase the capacity of, and to improve the heavyload discharge characteristics of alkaline batteries, in particularnickel-manganese batteries.

Furthermore, a subject matter of the present invention is to enhance theabove-described effects by controlling the ratio of a γ-type crystalstructure in nickel oxyhydroxide within a predetermined range.

The present invention relates to an alkaline battery comprising apositive electrode material mixture, a negative electrode, a separatorinterposed between the positive electrode material mixture and thenegative electrode, and an alkaline electrolyte, wherein the positiveelectrode material mixture includes a first active material comprisingnickel oxyhydroxide and a second active material comprising manganesedioxide, the nickel oxyhydroxide includes a γ-type crystal structure,the content of nickel in the nickel oxyhydroxide is not less than 45 wt%, and the average particle diameter on a volume basis of the nickeloxyhydroxide measured with a laser diffraction particle sizedistribution analyzer is 3 to 20 μm.

It is preferable that the nickel oxyhydroxide further includes a β-typecrystal structure.

It is preferable that the tap density of the nickel oxyhydroxide after500 times of tapping is not less than 1.5 g/cm³.

It is preferable that the content of water in the nickel oxyhydroxide isnot more than 3 wt %. It should be noted that water is considered to beadsorbed on the surface of the nickel oxyhydroxide.

It is preferable that the specific surface area of the nickeloxyhydroxide measured by a BET method is 10 to 30 m²/g.

It is preferable that when a powder X-ray diffraction pattern of thenickel oxyhydroxide includes a diffraction peak P_(γ) attributed to the(003) plane of a γ-type crystal having an interplanar spacing of 6.8 to7.1 angstroms (Å) and a diffraction peak P_(β) attributed to the (001)plane of a β-type crystal having an interplanar spacing of 4.5 to 5angstroms (Å), an integrated intensity I_(γ) of the diffraction peakP_(γ) and an integrated intensity I_(β) of the diffraction peak P_(β)satisfy 0.5≦I_(γ)/(I_(γ)+I_(β)). In this case, the average valence ofnickel included in the nickel oxyhydroxide is not less than 3.3.

It is preferable that when a powder X-ray diffraction pattern of thenickel oxyhydroxide includes a diffraction peak P_(γ) attributed to the(003) plane of a γ-type crystal having an interplanar spacing of 6.8 to7.1 angstroms (Å) and a diffraction peak P_(β) attributed to the (001)plane of a β-type crystal having an interplanar spacing of 4.5 to 5angstroms (Å), an integrated intensity I_(γ) of the diffraction peakP_(γ) and an integrated intensity I_(β) of the diffraction peak P_(β)satisfy 0.1≦I_(γ)/(I_(γ)+I_(β))<0.5. In this case, the average valenceof nickel included in the nickel oxyhydroxide is not less than 3.05 andless than 3.3.

It is preferable that the nickel oxyhydroxide is a solid solution inwhich an additive element is dissolved. In this case, it is preferablethat the additive element is at least one selected from the groupconsisting of manganese and cobalt.

It is preferable that when the nickel oxyhydroxide is a solid solutionin which manganese is dissolved as the additive element, the amount ofmanganese dissolved in the solid solution is 1 to 7 mol % of the totalof all the metallic elements included in the solid solution.

It is preferable that when the nickel oxyhydroxide is a solid solutionin which both manganese and cobalt are dissolved as the additiveelement, the amount of each of manganese and cobalt dissolved in thesolid solution is 1 to 7 mol % of the total of all the metallic elementsincluded in the solid solution.

It is further preferable that when the nickel oxyhydroxide is a solidsolution in which manganese is dissolved as the additive element, thesolid solution carries a cobalt oxide attached onto a surface thereof.In this case, it is preferable that the amount of manganese dissolved inthe solid solution is 1 to 7 mol % of the total of all the metallicelements included in the solid solution, and that the amount of thecobalt oxide is 0.1 to 7 wt % of the solid solution. It is alsopreferable that the average valence of cobalt included in the cobaltoxide is greater than 3.0.

Preferably, the content of the manganese dioxide in the positiveelectrode material mixture is 20 to 90 wt %.

The present invention also relates to a method for producing a positiveelectrode material for an alkaline battery.

The production method according to the present invention includes a fiststep of performing an operation of supplying a nickel (II) sulfateaqueous solution, a manganese (II) sulfate aqueous solution, a sodiumhydroxide aqueous solution and ammonia water into a reaction vesselprovided with a stirring blade through separate channels, while bubblingan inert gas and adjusting the temperature and pH in the reactionvessel, thereby obtaining nickel hydroxide including a β-type crystalstructure in which nickel sites are partly replaced with divalentmanganese.

The above-described method also includes a second step of washing withwater and drying the nickel hydroxide that has been obtained by thefirst step, followed by heating at 50 to 150° C. under an oxidizingatmosphere, thereby oxidizing manganese to an average valence of notless than 3.5.

The above-described method also includes a third step of introducing thenickel hydroxide that has been subjected to the second step into analkaline aqueous solution, together with an oxidizing agent, therebychemically oxidizing the nickel hydroxide.

It is preferable that, in the first step, hydrazine is further addedinto the reaction vessel to maintain a reducing atmosphere.

It is preferable that, in the second step, the average valence ofmanganese is set to not less than 3.8.

It is preferable that the oxidizing agent used in the third step ishypochlorite.

It is preferable that the alkaline aqueous solution used in the thirdstep is an aqueous solution in which at least one alkali salt selectedfrom the group consisting of potassium hydroxide, sodium hydroxide andlithium hydroxide is dissolved. In this case, it is preferable that theconcentration of the alkali salt in the alkaline aqueous solution is notless than 3 mol/L.

Hereinafter, nickel oxyhydroxide including a γ-type crystal structure isoccasionally referred to as “γ-nickel oxyhydroxide”, nickel oxyhydroxideincluding a β-type crystal structure as “β-nickel oxyhydroxide”, andnickel hydroxide including a β-type crystal structure as “β-nickelhydroxide”.

With the present invention, it is possible to increase the capacity ofan alkaline battery in which the positive electrode material mixturecontains nickel oxyhydroxide, while maintaining the advantage of havingexcellent heavy load discharge characteristics.

Controlling the content of nickel contained in γ-nickel oxyhydroxide andaverage particle diameter is particularly effective in increasing thecapacity of alkaline batteries.

By controlling the content of nickel and average particle diameter, thevolume energy density (mAh/cm³) of a positive electrode material mixturepellet comprising nickel oxyhydroxide and manganese dioxide can be byfar superior to that of the conventional ones using β-nickeloxyhydroxide and manganese dioxide. Accordingly, the capacity ofalkaline batteries increases significantly.

Additionally, dissolving an additive element in nickel oxyhydroxide isparticularly effective in improving the heavy load dischargecharacteristics of alkaline batteries.

As the additive element, manganese is particularly effective, and theuse of a solid solution nickel hydroxide in which a small amount ofmanganese is dissolved for a nickel oxyhydroxide source materialprovides a low redox potential, promotes the oxidation of the nickelhydroxide, and facilitates the production of a γ-type crystal structure.

Moreover, with the method for producing a positive electrode materialaccording to the present invention, manganate ions (MnO₄ ²⁻),permanganate ions (MnO₄ ⁻) or the like are difficult to be dissolvedinto the reaction atmosphere at the time of oxidizing nickel hydroxideto nickel oxyhydroxide. Accordingly, the degree of oxidation of nickeltends not to vary. In other words, with the production method of thepresent invention, manganese can be present in a stable state in nickeloxyhydroxide, so that the quality of the resulting battery can bemaintained stably.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view, partly in cross section, of an alkaline batteryaccording to the examples of the present invention.

FIG. 2 shows powder X-ray diffraction patterns of nickel oxyhydroxidesaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The alkaline battery according to the present invention comprises apositive electrode material mixture, a negative electrode, a separatorinterposed between the positive electrode material mixture and thenegative electrode, and an alkaline electrolyte. The positive electrodematerial mixture includes a first active material comprising nickeloxyhydroxide and a second active material comprising manganese dioxide,and the nickel oxyhydroxide includes a γ-type crystal structure.

From the viewpoint of increasing the capacity of the alkaline battery,it is necessary that the content of nickel in the nickel oxyhydroxideshould be not less than 45 wt %, preferably not less than 50 wt %.Further, from the viewpoint of enabling the production of the positiveelectrode material mixture pellet during actual manufacturing, it isnecessary that the average particle diameter on a volume basis measuredwith a laser diffraction particle size distribution analyzer should be 3to 20 μm, preferably 10 to 15 μm.

The nickel oxyhydroxide used in the present invention may comprise asingle phase including a γ-type crystal structure, or may comprise aeutectic material in which both a β-type crystal structure and a γ-typecrystal structure are present.

The γ-type crystal structure is a structure in which alkaline metal ions(ions A) are inserted between the NiO₂ layers constituting the nickeloxyhydroxide. In this structure, the electrical neutrality is maintainedamong the elements or ions, namely, A, H, Ni and O, constituting thenickel oxyhydroxide. γ-nickel oxyhydroxide is an oxide represented by achemical formula: A_(x)H_(y)NiO₂.nH₂O (J. Power Sources 8, p.229(1982)).

In a powder X-ray diffraction, γ-nickel oxyhydroxide provides adiffraction pattern described in the JCPDS inorganic material file, FileNo. 6-75. One example of the typical diffraction peaks is a diffractionpeak P_(γ) attributed to the (003) plane having a interplanar spacing of6.8 to 7.1 angstroms (Å). The (003) plane is a crystal plane that isperpendicular to the c-axis, and alkaline metal ions, water moleculesand the like are inserted between the interlayer spaces, therebyelongating the interlayer spaces to nearly 7 Å.

On the other hand, in a powder X-ray diffraction of β-nickeloxyhydroxide, a diffraction peak P_(β) attributed to the (001) planehaving an interplanar spacing of 4.5 to 5 Å is observed as a typicaldiffraction peak.

In terms of the amount of the positive electrode material mixture filledin the battery, the nickel oxyhydroxide used in the present inventionhas a tap density after 500 times of tapping of preferably not less than1.5 g/cm³, more preferably not less than 1.7 g/cm³.

Furthermore, from the viewpoint of maintaining, for example, thedistribution of the alkaline electrolyte in the positive electrodematerial mixture at a favorable state, allowing the discharge reaction(electrochemical reaction) of the nickel oxyhydroxide to proceedsmoothly, and increasing the high load discharge characteristics, thespecific surface area measured by using a BET method is preferably 10 to30 m²/g, more preferably 15 to 20 m²/g.

Further, the content of water in the nickel oxyhydroxide is preferablynot more than 3 wt %. It is particularly preferable to use nickeloxyhydroxide having a water content of not more than 2 wt %, since thisfacilitates the production of the positive electrode material mixturepellet.

When the above-described nickel oxyhydroxide includes a β-type crystalstructure, a powder X-ray diffraction pattern of the nickel oxyhydroxideincludes a diffraction peak P_(β) attributed to the (001) plane of aβ-type crystal having an interplanar spacing of about 4.5 to 5 Å, inaddition to the above-described diffraction peak P_(γ) attributed to the(003) plane of a γ-type crystal.

When the integrated intensity I_(γ) of the diffraction peak P_(γ) andthe integrated intensity I_(β) of the diffraction peak P_(β) satisfy0.5≦I_(γ)/(I_(γ)+I_(β)), a significant effect of increasing the capacityis achieved. Specifically, the average valence of nickel included in thenickel oxyhydroxide becomes not less than 3.3. When the average valenceof nickel included in the nickel oxyhydroxide is not less than 3.3,γ-nickel oxyhydroxide provides a large amount of the discharge capacitycorresponding to their valence, making it possible to achieve asignificant increase in the capacity of the battery.

On the other hand, when I_(γ)/(I_(γ)+I_(β)) is less than 0.5, it ispossible to increase the capacity, but the effect thereof is reduced. Inthis case, the average valence of nickel included in the nickeloxyhydroxide is not less than 3.05 and less than 3.3. However, in thecase where 0.1≦I_(γ)/(I_(γ)+I_(β))<0.5, the bulk density (tap density)of the particles can be maintained high, and therefore, there is anadvantage that the positive electrode material mixture pellet is easy toproduce and can be readily filled in the battery.

Generally, in the case of obtaining nickel oxyhydroxide by highlyoxidizing nickel hydroxide, it is often the case that a eutecticmaterial of β-nickel oxyhydroxide (the main component) and a smallamount of γ-nickel oxyhydroxide is obtained which shows littleelongation of the interlayer spaces of the crystal planes perpendicularto the c-axis. However, the present invention also gives importance tothe cases where a single phase of γ-nickel oxyhydroxide, or a eutecticmaterial of γ-nickel oxyhydroxide (the main component) and a smallamount of β-nickel oxyhydroxide, is actively used as the positiveelectrode material.

Nickel oxyhydroxide including a γ-type crystal structure does notnecessarily have a discharge capacity corresponding to its nickelvalence. As compared with β-nickel oxyhydroxide, γ-nickel oxyhydroxideoften may cause a significant decrease in the discharge voltage, andthus fails to provide a sufficient capacity.

Therefore, the present invention proposes the use of a solid solution inwhich an additive element such as manganese is dissolved, as the nickeloxyhydroxide including a γ-type crystal structure. A solid solutionnickel oxyhydroxide in which an additive element is dissolved can besynthesized by oxidizing a solid solution nickel hydroxide in which anadditive element is dissolved. As the additive element, cobalt can bepreferably used, in addition to manganese.

A solid solution γ-nickel oxyhydroxide in which manganese is dissolvedcan provide a sufficient capacity during reducing highly oxidized nickelto a valence near 2 in a relatively high potential region, although thedetailed reaction mechanism has not been elucidated. Since it ispossible to utilize the discharge reaction of nickel involving more thanone electron, the use of the nickel oxyhydroxide including a γ-typecrystal structure and in which manganese is dissolved, as the positiveelectrode material is effective in increasing the battery capacity. Thepresence of manganese allows the oxidation state of the nickeloxyhydroxide, i.e., the amount of electricity held, to be improvedsufficiently.

When manganese is dissolved in nickel oxyhydroxide to form a solidsolution, the redox potential at which nickel becomes divalent toquadrivalent shifts to a lower value. Furthermore, quadrivalentmanganese ions that are present in the nickel layers of the nickeloxyhydroxide stabilize the γ-type crystal structure thermodynamically.Accordingly, at the time of synthesizing the nickel oxyhydroxide, theratio of the γ-type crystal structure that is produced becomes high, andit is therefore possible to obtain nickel oxyhydroxide having a highaverage valence of nickel.

When cobalt is dissolved in nickel oxyhydroxide to form a solidsolution, a defect that is suitable for proton diffusion can be formedin the crystal (NiO₂ layers) during the discharge process of nickel.Moreover, the electron conductivity of the nickel oxyhydroxide itself isimproved. Accordingly, it is possible to significantly increase thecapacity of the alkaline battery, without impairing the heavy loaddischarge characteristics.

Although the nickel oxyhydroxide is preferably a solid solution in whichat least one of manganese and cobalt is dissolved, it is more preferablya solid solution in which both manganese and cobalt are dissolved. Whenboth manganese and cobalt are dissolved in the nickel oxyhydroxide, itis possible to increase both the effect of increasing the capacity andimproving the heavy load discharge characteristics at the same time.

When the nickel oxyhydroxide is a solid solution in which manganese isdissolved as the additive element, the amount of manganese dissolved inthe solid solution is preferably 1 to 7 mol % of the total of all themetallic elements contained in the solid solution. When the amount ofmanganese is less than 1 mol %, only a little effect of the additiveelement can be obtained. On the other hand, in the viewpoint of avoidinga decrease in the battery capacity, the amount of manganese ispreferably not more than 7 mol %.

When the nickel oxyhydroxide is a solid solution in which cobalt isdissolved as the additive element, the amount of cobalt dissolved in thesolid solution is preferably 1 to 7 mol % of the total of all themetallic elements contained in the solid solution. When the amount ofcobalt is less than 1 mol %, only a little effect of the additiveelement can be obtained. On the other hand, from the viewpoint ofavoiding a decrease in the battery capacity, the amount of cobalt ispreferably not more than 7 mol %.

When the nickel oxyhydroxide is a solid solution in which both manganeseand cobalt are dissolved as the additive element, the amount of each ofmanganese and cobalt dissolved in the solid solution is preferably 1 to7 mol % of the total of all the metallic elements contained in the solidsolution.

From the viewpoint of maintaining the heavy load dischargecharacteristics, it is also effective to attach a cobalt oxide to thesurface of the nickel oxyhydroxide. The cobalt oxide attached onto thesurface of the nickel oxyhydroxide serves to maintain a favorablecurrent collecting state from the active material during the dischargeof the γ-nickel oxyhydroxide that involves a volume change, thusmaintaining the heavy load discharge characteristics.

From the viewpoint of maintaining a favorable current collecting statefrom the active material, the amount of the cobalt oxide is preferablynot less than 0.1 wt % of the nickel oxyhydroxide. In addition, from theviewpoint of suppressing the dissolution of cobalt at the time ofstoring the battery at a high temperature to ensure the stability(reliability) of the positive electrode, the amount of the cobalt oxideis preferably not more than 7 wt % of the nickel oxyhydroxide.

The average valence of cobalt included in the cobalt oxide is preferablygreater than 3.0. A cobalt oxide in which the average valence of cobaltis greater than 3.0 has extremely higher electron conductivity than acobalt oxide in which the average valence of cobalt is not more than3.0. Accordingly, it is possible to maximize the current collectionefficiency from the nickel oxyhydroxide. Such a cobalt oxide alsoinhibits cobalt from being reduced to a valence of 2 or dissolved intothe electrolyte when the discharged battery is left (stored). Therefore,by using nickel oxyhydroxide with such a cobalt oxide attached onto thesurface, it is also possible to improve the storage characteristics(reliability) of the battery, in addition to increasing the capacity andimproving the heavy load discharge characteristics.

Manganese dioxide can be more easily filled in the battery case at ahigh density than nickel oxyhydroxide, and the price of manganesedioxide is low. In view of these facts, the content of the manganesedioxide in the positive electrode material mixture is not less than 20wt %. Further, from the viewpoint of increasing the battery capacity,the content of the manganese dioxide in the positive electrode materialmixture is preferably not more than 90 wt %.

Nickel oxyhydroxide including a γ-type structure can be obtained bychemically oxidizing nickel hydroxide composed mainly of a β-typestructure in an alkaline aqueous solution using an oxidizing agent, andwashing this with water and drying.

Here, according to a Bode diagram (Electrochemical Acta 11, p.1079(1966)) relating to the charge/discharge of commonly used nickelhydroxide, it seems that nickel oxyhydroxide composed mainly of a γ-typestructure can be easily obtained when nickel hydroxide (α-3Ni(OH)₂.2H₂O)with an α-type structure is used as the starting material.

However, nickel hydroxide including an α-type structure generally isextremely bulky, and its interplanar distance for the (003) planesperpendicular to the c-axis is more than 8 angstroms, and thisinterplanar distance is larger than that of γ-nickel hydroxide.Therefore, the shape (hysteresis) of the source material is reflected onnickel oxyhydroxide including a γ-type structure that is obtained byoxidizing nickel hydroxide including an α-type structure; accordingly,the material has an increased porosity, and it is therefore not possibleto achieve powder with high density.

Therefore, the present invention proposes the use of nickel hydroxidecomposed mainly of a high-density β-type structure (e.g., nickelhydroxide not less than 90 wt % of which is composed of a β-typestructure), as the source material of nickel oxyhydroxide including aγ-type structure. Nickel oxyhydroxide composed mainly of a γ-typestructure is relatively dense, and thus is effective for filling theactive material in the battery at a high density.

As the alkaline aqueous solution, it is preferable to use at least oneselected from the group consisting of potassium hydroxide, sodiumhydroxide and lithium hydroxide. A reaction that forms nickeloxyhydroxide composed mainly of a γ-type structure proceeds, while beingaccompanied by insertion of alkaline metal ions into the NiO₂ layers.For this reason, the reaction proceeds more smoothly, when theconcentration of alkali salts that are present together with theoxidizing agent is high. Therefore, the concentration of these alkalisalts in the alkaline aqueous solution is preferably not less than 3mol/L.

The nickel hydroxide composed mainly of a β-type structure for use asthe source material of nickel oxyhydroxide including a γ-type structureis preferably a solid solution in which manganese is dissolved.

The redox potential of a solid solution nickel hydroxide in whichmanganese is dissolved shifts to a lower value than that of commonlyused nickel hydroxide, so that it tends to be highly oxidized to form aγ-type structure in a treatment using an oxidizing agent.

As compared with the state in which manganese is present as an oxide innickel hydroxide and forms a eutectic material with the nickelhydroxide, the state of a solid solution in which manganese is dissolvedin nickel hydroxide is superior in that leaching out of manganese hardlyoccurs during the treatment using an oxidizing agent.

Further, as compared with the state of a solid solution in whichmanganese is inserted into a location other than the nickel sites in thenickel hydroxide crystal, the state of a solid solution in whichmanganese is substituted for the nickel sites of the nickel hydroxide issuperior in that leaching out of manganese hardly occurs during thetreatment using an oxidizing agent.

In addition, when manganese is leached out as manganate ions (MnO₄ ²⁻),permanganate ions (MnO₄ ⁻) or the like at the time of treating thenickel hydroxide with an oxidizing agent, the degree of oxidation ofnickel varies. In the case of using a solid solution nickel hydroxide inwhich nickel sites are partly replaced with manganese, such a phenomenonis prevented, and thus leaching out of manganese hardly occurs.

The average valence of manganese in the β-nickel hydroxide immediatelybefore the treatment with an oxidizing agent is preferably not less than3.5, more preferably not less than 3.8. When the average valence ofmanganese is as low as 2 to 3, a manganese oxide might be liberatedlocally in the nickel oxyhydroxide particles. Although the details ofthe reason are not known, manganese species, for example, move in thecrystal during the oxidation treatment, thereby forming an oxide. Inthat case, it is difficult to obtain γ-nickel oxyhydroxide havingdischarge efficiency that is high enough to contribute to an increase inthe battery capacity. Therefore, the average valence of manganese ispreferably close to 4.

Next, an example of the efficient method for producing nickeloxyhydroxide including a γ-type crystal structure and in which manganeseis dissolved in a suitable state will be described.

First Step

First, a nickel (II) sulfate aqueous solution, a manganese (II) sulfateaqueous solution, a sodium hydroxide aqueous solution and ammonia waterare supplied into a reaction vessel provided with a stirring bladethrough separate channels. This operation is carried out while bubblingan inert gas in the reaction vessel and adjusting the temperature and pHin the reaction vessel. Through this operation, it is possible toprovide nickel hydroxide having a β-type crystal structure and in whichnickel sites are partly replaced with divalent manganese.

The concentrations of the solutions to be supplied to the reactionvessel need to be appropriately adjusted by a person with the ordinaryskill in the art, according to the equipment such as the reactionvessel, and such an adjustment can be performed freely by a personskilled in the art. Examples of the commonly used concentrations include0.5 to 2 mol/L for nickel (II) sulfate, 1 to 5 mol/L for sodiumhydroxide, and 10 to 30 wt % for ammonia water; however, theconcentrations are not limited to these. The concentration of manganese(II) sulfate may be selected such that the desired content of nickel canbe achieved.

Nitrogen, argon or the like is used as the inert gas. By stirring thesource material solutions while bubbling the inert gas, nickel andmanganese that are in a divalent state form an ammine complex, and thesodium hydroxide aqueous solution that is excessively supplied to theammine complex exert an action, thereby precipitating nickel hydroxidecomposed mainly of a β-type structure and in which divalent nickel sitesare partly replaced with manganese. Nickel hydroxide in which manganeseis dissolved may decrease in density in many cases, and the main causeof this is that divalent manganese ions are oxidized in the middle ofthe production of the nickel hydroxide. On the other hand, a β-nickelhydroxide with a very high density can be obtained by performing thesynthesis under an inert gas atmosphere as described above.

From the viewpoint of maintaining a reducing atmosphere in the reactionvessel, it is preferable that, in the first step, hydrazine is furtheradded into the reaction vessel. By controlling the atmosphere in such amanner, the oxidation of manganese ions during synthesis is suppressedeven further, making it possible to reliably obtain β-nickel hydroxidein which divalent manganese is substituted for a portion of the nickelsites.

Second Step

Next, the β-nickel hydroxide obtained by the fist step is washed withwater, dried, and heated at 50 to 150° C. under an oxidizing atmosphere.Through this operation, only manganese can be oxidized to an averagevalence of not less than 3.5.

When the valence of manganese in the β-nickel hydroxide remains at 2, amanganese oxide might be liberated locally in the nickel oxyhydroxideparticles during storage at room temperature and atmospheric pressurebefore the oxidation treatment, or during the oxidation treatment, sothat sufficient characteristics may not be obtained at a later time. Onthe other hand, when manganese is converted into a state of a valence of3.5 or more after the first step, manganese can be stably present in thenickel sites of the β-nickel hydroxide.

Third Step

Next, the nickel hydroxide that has undergone the second step isintroduced into an alkaline aqueous solution, together with an oxidizingagent, and thereby the nickel hydroxide is chemically oxidized. Throughthis operation, it is possible to obtain nickel oxyhydroxide including aγ-type crystal structure.

In γ-nickel oxyhydroxide, alkali metal ions are inserted between theNiO₂ layers of the nickel oxyhydroxide, thus maintaining the electricalneutrality of tetravalent nickel ions. Therefore, it is necessary toperform the treatment using an oxidizing agent in an aqueous solutioncontaining alkali metal ions. However, since most anion species otherthan OH⁻ (e.g., SO₄ ²⁻, NO₃ ⁻ and Cl⁻) adversely affect the batterycharacteristics, it is practically essential that the treatment beperformed in an alkaline aqueous solution.

As the alkaline aqueous solution, it is preferable to use at least onealkali salt selected from the group consisting of potassium hydroxide,sodium hydroxide and lithium hydroxide, as described above. Furthermore,from the viewpoint of improving the production efficiency of theγ-nickel oxyhydroxide, the concentration of the alkali salt in thealkaline aqueous solution is preferably not less than 3 mol/L.

As the oxidizing agent for oxidizing nickel hydroxide to nickeloxyhydroxide, it is possible to use, for example, hypochlorites such assodium hypochlorite, persulfates such as potassium peroxydisulfate,halogens such as bromine, and a hydrogen peroxide solution. Among them,hypochlorites are most suitable, since they are highly oxidative,stable, and low in price.

Hereinafter, the present invention will be described specifically by wayof examples.

First, the method for measuring the physical properties of nickeloxyhydroxide, or a source material nickel hydroxide will be described.

<1> Powder X-Ray Diffraction Measurement

X-ray diffraction profiles (diffraction patterns) of the various typesof powder were obtained for the range of 2θ=10 to 70 degrees (deg.)under the measurement conditions described below, using a powder X-raydiffraction apparatus “RINT1400” manufactured by Rigaku Corporation.

(Anticathode) Cu

(Filter) Ni

(Tube voltage) 40 kV

(Tube current) 100 mA

(Sampling angle) 0.02 deg.

(Scanning rate) 3.0 deg./min.

(Divergence slit) ½ deg.

(Scattering slit) ½ deg.

From each of the diffraction patterns, an integrated intensity I_(γ) ofa diffraction peak P_(γ) attributed to the (003) plane of a γ-typecrystal having an interplanar spacing near 6.8 to 7.1 Å, and anintegrated intensity I_(β) of a diffraction peak P_(β) attributed to the(001) plane of a β-type crystal having an interplanar spacing of 4.5 to5 Å were obtained, and then the value of I_(γ)/(I_(γ)+I_(β)) wasobtained.

<2> Nickel Content

The content of nickel in each of the sample powders was determined bythe following chemical measurement based on a gravimetric method.

A nitric acid aqueous solution was added to a sample powder of nickeloxyhydroxide or nickel hydroxide, and the whole was heated to dissolvethe particles completely, followed by adding a tartaric acid aqueoussolution and ion exchanged water to adjust the volume. After the pH ofthis solution was adjusted using ammonia water and acetic acid,potassium bromate was added, and thereby the additive element (manganeseions or cobalt ions) that could cause measurement error was brought intoa higher oxidation state.

Next, an ethanol solution of dimethylglyoxime was added to this solutionunder stirring, thus precipitating the nickel (II) ions as a complexcompound of dimethylglyoxime. Subsequently, suction filtration wasperformed, and the produced precipitate was collected and dried in anatmosphere at 110° C., and the weight of the precipitate was measured.From the measurement result, the content of nickel in each of thepowders was calculated using the following expression:Content of nickel (wt %)={weight of precipitate (g)×0.2032}/{weight ofsample powder (g)}<3> Average Valence of Nickel

When the nickel oxyhydroxide did not contain any additive element suchas manganese or cobalt, potassium iodide and sulfuric acid are added tothe sample powder of the nickel oxyhydroxide, and they were completelydissolved by performing continuous stirring sufficiently. During thisprocess, nickel ions having a high valence oxidized the potassium iodideto librate iodine, and the nickel ions themselves were reduced to avalence of 2. Subsequently, the iodine that had been produced andliberated was titrated using a 0.1 mol/L sodium thiosulfate aqueoussolution. The titer at this time reflected the amount of nickel ionshaving a valence greater than 2. Using the result of the titration andthe content of nickel obtained in <2> described above, the averagevalence of the nickel included in the nickel oxyhydroxide was calculatedwith the following expression:Average valence of nickel={titer (L)×0.1 (mol/L)×58.69}/{weight ofnickel oxyhydroxide (g)×content of nickel}+2.00

When the nickel oxyhydroxide is a solid solution containing an additiveelement (manganese or cobalt), manganese ions or cobalt ions having ahigh valence also oxidize the potassium iodide to librate iodine, andthe manganese ions or cobalt ions themselves are reduced to a valence of2, so that it is necessary to make a correction for this.

Therefore, in the case of a solid solution nickel oxyhydroxide in whichan additive element was dissolved, a nitric acid aqueous solution wasadded to this and heating was performed to completely dissolve theparticles, and thereafter, ICP emission spectrometry was performed onthe resulting solution to quantify the content of the additive element.For the ICP emission spectrometry, a VISTA-RL manufactured by VARIAN,INC. was used. Assuming that the average valence of manganese includedin the nickel oxyhydroxide was 4, and the average valence of cobalt was3.5, the above-described titer was corrected using the result of the ICPemission spectrometry, thereby calculating the average valence of thenickel.

In addition, the average valence of manganese included in the solidsolution of the source material nickel hydroxide before it had beenoxidized to the nickel oxyhydroxide was determined by a redox titrationthat was basically the same as described above, using the values of thecontents of the additive elements obtained by the ICP emissionspectrometry, and assuming that nickel was divalent and cobalt wasdivalent.

<4> Tap Density

For the measurement of the tap density, a measurement apparatus “PowderTester PT-R” manufactured by Hosokawa Micron Corporation was used. Usinga sieve with a mesh opening of 100 μm as the sieve for passing thesample powders through, each powder was dropped into a 20 cc tappingcell. After the cell was filled up, tapping was carried out 500 times ata rate of one time per second with a stroke length of 18 mm. Thereafter,the tap density was measured.

<5> Average Particle Diameter

Using a Microtrack particle size distribution measurement apparatus“9220 FRA” manufactured by NIKKISO CO., LTD., each sample powder wassufficiently dispersed in water, and the average particle diameter D₅₀on a volume basis was determined by a laser diffraction method.

<6> Water Content

Using a dry measure type moisture meter “CZA-2100” manufactured by CHINOCORPORATION, 5 g of each sample powder was heat-dried at 120° C., andthereafter, the content of water (wt %) in the sample was measured.

<7> BET Specific Surface Area

After About 2 g of each sample powder was preliminarily dried by beingevacuated for six hours under heating at 60° C., a nitrogen gas wasadsorbed by the sample, and the absorbed amount was measured using an“ASAP2010” manufactured by Micromeritics Instrument Corporation.Furthermore, the weight of the sample powder was precisely weighed, andthe specific surface area was determined by a BET method.

EXAMPLE 1

[1] Production of Nickel Hydroxide

(1) Nickel Hydroxide a1

A nickel (II) sulfate aqueous solution, a sodium hydroxide aqueoussolution and ammonia water having predetermined concentrations wereprepared. They were supplied with pumps into a reaction vessel providedwith a stirring blade such that the pH in the vessel was constant, andcontinuous stirring was performed sufficiently, thereby precipitatingand growing spherical β-nickel hydroxide.

Subsequently, the resulting particles were heated in a sodium hydroxideaqueous solution that was different from the one described above toremove sulfate ions, followed by washing with water and drying, therebyproducing a nickel hydroxide a1.

(2) Nickel Hydroxide b1

Pure water and a small amount of hydrazine (reducing agent) were addedinto a reaction vessel provided with a stirring blade, and bubbling witha nitrogen gas was started. Additionally, a nickel (II) sulfate aqueoussolution, a manganese (II) sulfate aqueous solution, a sodium hydroxideaqueous solution and ammonia water having predetermined concentrationswere prepared. They were supplied with pumps into the above-describedreaction vessel such that the pH in the vessel was constant, andcontinuous stirring was performed sufficiently, thereby precipitatingand growing a solid solution comprising spherical β-nickel hydroxide inwhich manganese was dissolved.

Subsequently, the resulting particles were heated in a sodium hydroxideaqueous solution that was different from the one described above toremove sulfate ions, followed by washing with water and vacuum drying,and they were further subjected to air oxidation at 80° C. for 72 hours,thereby producing a nickel hydroxide b1

composition: Ni_(0.95)M_(0.05)(OH)₂

. Here, the air oxidation was a treatment for oxidizing only Mn to avalence near 4

(3) Nickel Hydroxide c1

Pure water and a small amount of hydrazine (reducing agent) were addedinto a reaction vessel provided with a stirring blade, and bubbling witha nitrogen gas was started. Additionally, a nickel (II) sulfate aqueoussolution, a manganese (II) sulfate aqueous solution, a cobalt (II)sulfate aqueous solution, a sodium hydroxide aqueous solution andammonia water having predetermined concentrations were prepared. Theywere supplied with pumps into the above-described reaction vessel suchthat the pH in the vessel was constant, and continuous stirring wasperformed sufficiently, thereby precipitating and growing a solidsolution comprising spherical β-nickel hydroxide in which manganese andcobalt were dissolved.

Subsequently, the resulting particles were heated in a sodium hydroxideaqueous solution that was different from the one described above toremove sulfate ions, followed by washing with water and vacuum drying,and they were further subjected to air oxidation at 80° C. for 72 hours,thereby producing a nickel hydroxide c1

composition: Ni_(0.90)Mn_(0.05)Co_(0.05)(OH)₂

.

(4) Nickel Hydroxide d1

After the nickel hydroxide b1 was introduced into a cobalt sulfateaqueous solution in a reaction vessel, a sodium hydroxide aqueoussolution was gradually added thereto, and the whole was continuouslystirred at 35° C. while adjusting the pH in the vessel such that it wasmaintained at 10, thus precipitating cobalt hydroxide on the surface ofthe solid solution particles. Thereby, a nickel hydroxide d1 wasproduced, which was the nickel hydroxide b1 coated with Co(OH)₂. Thenickel hydroxide d1 was washed with water, and thereafter subjected tovacuum drying.

Here, the amount of the cobalt hydroxide attached onto the surface ofthe nickel hydroxide b1 was 5.0 parts by weight per 100 parts by weightof the nickel hydroxide b1.

Each of the nickel hydroxides a1 to d1 had an average particle diameterof about 12 μm, a BET specific surface area in the range of 10 to 12m²/g, a tap density in the range of 2.1 to 2.2 g/cm³.

[2] Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

After 200 g of the nickel hydroxide a1 was introduced into 1 L of a 5mol/L sodium hydroxide aqueous solution, a sufficient amount of a sodiumhypochlorite aqueous solution (effective chlorine concentration: 5 wt %)serving as an oxidizing agent was added thereto, and the whole wasstirred to convert the nickel hydroxide to nickel oxyhydroxide. Theresulting particles were sufficiently washed with water, followed byvacuum drying at 60° C. (24 hours), thereby producing a nickeloxyhydroxide A1.

Further, nickel oxyhydroxides B1, C1 and D1 were produced by performinga process similar to that described above, using the nickel hydroxidesb1, c1 and d1, respectively, in place of the nickel hydroxide a1.

[3] Analysis of Physical Properties of Nickel Oxyhydroxides

Table 1 shows the values of I_(γ)/(I_(γ)+I_(β)) and the average valencesof nickel obtained for the nickel oxyhydroxides A1 to D1. TABLE 1Average Nickel hydroxide I_(γ)/(I_(γ) + I_(β)) valence Nickeloxyhydroxide source material value of nickel Nickel oxyhydroxide A1Nickel hydroxide a1 0.08 3.04 Nickel oxyhydroxide B1 Nickel hydroxide b10.79 3.41 Nickel oxyhydroxide C1 Nickel hydroxide c1 0.81 3.40 Nickeloxyhydroxide D1 Nickel hydroxide d1 0.78 3.41

From Table 1, the following can be stated.

First, in the case of the nickel oxyhydroxide A1, which contained nomanganese or cobalt, the production ratio of the γ-nickel oxyhydroxidewas very small, and the chemical oxidation of nickel was suppressed tosuch a level that the valence was near 3.

On the other hand, in each of the cases of the solid solution nickeloxyhydroxides B1 to D1, in which manganese was dissolved, the value ofI_(γ)/(I_(γ)+I_(β)) was near 0.8, and the average valence of nickel wasincreased to about 3.4.

[4] Fabrication of Alkaline Battery

Nickel-manganese batteries as primary batteries were fabricated usingthe nickel oxyhydroxides A1 to D1, respectively. FIG. 1 is a front view,partly in cross section, of a battery fabricated in this example.

The batteries using the nickel oxyhydroxides A1 to D1 were namedbatteries A1 to D1, respectively.

(1) Production of Positive Electrode Material Mixture Pellet

Predetermined nickel oxyhydroxide, manganese dioxide and graphite weremixed at a weight ratio of 50:50:5, and zinc oxide was added to themixture, in an amount corresponding to 5 wt % of the nickel oxyhydroxidea2. Further, 1 part by weight of an alkaline electrolyte (a 40 wt %potassium hydroxide aqueous solution) was added, per 100 parts by weightof the total of the nickel oxyhydroxide a2 and the manganese dioxide.Thereafter, the mixture was formed into particulates by stirring andmixing the mixture in a mixer until it became homogeneous. The resultingparticulates were molded into the shape of a hollow short cylinder,thereby producing a positive electrode material mixture pellet.

(2) Assembly of Batteries

A nickel-plated steel plate was used for a positive electrode case 1. Agraphite coating film 2 was formed on the inner surface of the positiveelectrode case 1. A plurality of positive electrode material mixturepellets 3 in the shape of a short cylinder were inserted inside thepositive electrode case 1. The positive electrode material mixturepellets 3 were re-pressurized inside the positive electrode case 1 so asto be closely attached onto the inner surface of the positive electrodecase 1. A cylindrical separator 4 was inserted inside the positiveelectrode material mixture pellets 3, and an insulating cap 5 was placedon the inner bottom surface of the positive electrode case 1.Thereafter, an alkaline electrolyte was injected into the positiveelectrode case 1, in order to wet the separator 4 and the positiveelectrode material mixture pellets 3. An aqueous solution containing 40wt % of potassium hydroxide was used as the alkaline electrolyte. Afterinjection of the electrolyte, a gelled negative electrode 6 was filledinside the separator 4. A mixture of sodium polyacrylate serving as agelling agent, the alkaline electrolyte and zinc powder serving as anegative electrode active material was used for the gelled negativeelectrode 6.

Next, a negative electrode current collector 10 integrally formed with asealing plate 7 made of resin, a bottom plate 8 serving as a negativeelectrode terminal, and an insulating washer 9 was inserted into thegelled negative electrode 6. Then, the opening end of the positiveelectrode case 1 was clamped to the periphery of the bottom plate 8,with the end of the sealing plate 7 disposed therebetween, thus sealingthe opening of the positive electrode case 1. The outer surface of thepositive electrode case 1 was covered with an outer jacket label 11.Thus, an AA-sized nickel-manganese battery as shown in FIG. 1 wascompleted.

[5] Evaluation of Alkaline Batteries

Each of the thus fabricated nickel-manganese batteries A1 to D1 wascontinuously discharged at 20° C. with a constant current of 50 mA, andthe discharge capacity obtained during a period in which the batteryvoltage reached 0.9 V was measured.

In addition, each of the batteries in the initial state was continuouslydischarged at 20° C. with a constant power of 1 W, and the dischargecapacity obtained during a period in which the battery voltage reached0.9 V was also measured.

The results obtained were shown together in Table 2. It should be notedthat in both the 50 mA discharge and the 1 W discharge, the dischargecapacity of each of the nickel-manganese batteries B1 to D1 was shown asa relative value, taking the discharge capacity of the nickel-manganesebattery A1 as 100. TABLE 2 1 W 50 mA discharge discharge Type of batteryNickel oxyhydroxide capacity capacity Battery A1 Nickel oxyhydroxide A1100 100 Battery B1 Nickel oxyhydroxide B1 120  98 Battery C1 Nickeloxyhydroxide C1 120 117 Battery D1 Nickel oxyhydroxide D1 121 116

From Table 2, the following can be stated:

First, in the case of the batteries using the nickel oxyhydroxides B1 toD1, in which manganese was dissolved to increase the average valence ofnickel to about 3.4, a high capacity corresponding to the high valencewas obtained when the batteries were continuously discharged with aconstant current of 50 mA (low load). That is, the capacity of thebatteries B1 to D1 could be increased to a higher level than that of thebattery A1 using the nickel oxyhydroxide A1, which was composed mainlyof the β-nickel oxyhydroxide.

However, for the continuous discharge with 1 W (heavy load), thecapacity of the battery B1 using the nickel oxyhydroxide B1, in whichonly manganese was dissolved, was lower than that of the battery A1using the nickel oxyhydroxide A1.

The reason seems to be that the heavy load discharge characteristicswere greatly reduced, for example, due to the following reasons(controlling factors): (a) the redox potential (equilibrium potential)of the γ-nickel oxyhydroxide is lower than that of the β-nickeloxyhydroxide; (b) the γ-nickel oxyhydroxide undergoes a large volumechange (change in the crystal structure) during discharge, and thereforehas a high degree of polarization; and (c) the electron conductivity ofthe γ-nickel oxyhydroxide in which only manganese is dissolved greatlydecreases with discharge.

In contrast, the battery C1 using the nickel oxyhydroxide C1, in whichmanganese and cobalt were dissolved, provided a high discharge capacityin both the 50 mA (low load) discharge and the 1 W (heavy load)discharge.

In this case, the discharge capacity seems to have been improved sincethe γ-type crystal structure was stabilized thermally due to thepresence of the manganese ions (quadrivalent) added inside the nickellayers, thus increasing the average valence of nickel in the nickeloxyhydroxide.

Further, when cobalt is added in the nickel oxyhydroxide, a defect thatis suitable for proton diffusion can be formed in the NiO₂ layers duringthe discharge process of nickel, and the electron conductivity of thenickel oxyhydroxide itself also improves at the same time. Accordingly,the electron conductivity of the nickel oxyhydroxide can also bemaintained at a high level during discharge, so that the heavy loaddischarge characteristics are considered to be significantly improved.

It is inferred that the battery C1 using the solid solution nickeloxyhydroxide C1, in which both manganese and cobalt were dissolved,provided a high capacity both for the low load and heavy load dischargesfor these reasons.

In addition, the battery D1 whose surface was covered with a cobaltoxide and that used the nickel oxyhydroxide D1, in which manganese wasdissolved, also provided a high discharge capacity in both the 50 mA(low load) discharge and the 1 W (heavy load) discharge.

In connection with this, another test was carried out, in which Co(OH)₂that had been synthesized at a pH near 10 was introduced into a 5 mol/Lsodium hydroxide, to which a sodium hypochlorite aqueous solution wasadded to convert the Co(OH)₂ into a cobalt oxide. Then, as a result ofexamining the average valence of cobalt in the resulting cobalt oxide,it was confirmed that the cobalt was oxidized to a valence greater than3, and had very high electron conductivity.

The nickel oxyhydroxide D1 had a cobalt oxide having high electronconductivity attached onto the surface of the particles comprising thenickel oxyhydroxide, and therefore seems to have been able to maintainrelatively favorable current collection between the active materialseven during the discharge of the γ-nickel oxyhydroxide, which underwenta volume change. Accordingly, it seems that the degree of polarizationwas reduced, thus increasing the capacity and improving the heavy loaddischarge characteristics at the same time.

As described above, with the present invention, alkaline batterieshaving a high capacity and excellent heavy load dischargecharacteristics could be obtained.

EXAMPLE 2

In order to optimize the average valence of nickel in the nickeloxyhydroxide, the value of I_(γ)/(I_(γ)+I_(β)) and the content of themanganese dioxide in the positive electrode material mixture, thefollowing tests and evaluations were performed.

[1] Production of Nickel Oxyhydroxide

After 200 g of the nickel hydroxide c1

composition: Ni_(0.90)Mn_(0.05)Co_(0.05)(OH)₂

used in Example 1 was introduced into 1 L of a 0.5 mol/L sodiumhydroxide aqueous solution, a sufficient amount of a sodium hypochloriteaqueous solution (effective chlorine concentration: 5 wt %) serving asan oxidizing agent was added thereto, and the whole was stirred toconvert the nickel hydroxide to nickel oxyhydroxide. The resultingparticles were sufficiently washed with water, followed by vacuum dryingat 60° C. (24 hours), thereby producing a nickel oxyhydroxide C₁.

Further, nickel oxyhydroxides C₂ to C₆ were produced in the same manneras described above, except for changing the concentration of the sodiumhydroxide aqueous solution to 1.0 mol/L, 3.0 mol/L, 4.0 mol/L, 5.0 mol/Land 7.0 mol/L, respectively.

[2] Analysis of Physical Properties of Nickel Oxyhydroxides

Table 3 summarizes the values of I_(γ)/(I_(γ)+I_(β)) obtained by powderX-ray diffraction and the average valences of nickel obtained by achemical analysis for the resulting nickel oxyhydroxides C₁ to C₆

From Table 3, it can be seen that the degree of oxidation of the nickeloxyhydroxide (the production ratio of the γ-nickel oxyhydroxide and theaverage valence of nickel) could be controlled by adjusting theconcentration of the sodium hydroxide aqueous solution that was presentat the time of the chemical oxidation. TABLE 3 Concentration ofI_(γ)/(I_(γ) + NaOH aqueous I_(β)) Average valence Nickel oxyhydroxidesolution value of nickel Nickel oxyhydroxide C₁ 0.5M 0.11 3.09 Nickeloxyhydroxide C₂ 1.0M 0.32 3.24 Nickel oxyhydroxide C₃ 3.0M 0.53 3.31Nickel oxyhydroxide C₄ 4.0M 0.68 3.36 Nickel oxyhydroxide C₅ 5.0M 0.813.40 Nickel oxyhydroxide C₆ 7.0M 0.98 3.58[3] Fabrication of Alkaline Batteries

Positive electrode material mixtures C_(1n) to C_(6n) (n is an integerof 1 to 8) were prepared using the nickel oxyhydroxides C₁ to C₆, andthey were used to produce nickel-manganese batteries C_(1n) to C_(6n) (nis an integer of 1 to 8), respectively, serving as primary batteries.

Here, from the viewpoint of optimizing the content of the manganesedioxide in the positive electrode material mixture, the content of themanganese dioxide in the positive electrode material mixture (the weightratio of manganese dioxide to the entire positive electrode materialmixture, including, for example, graphite serving as a conductive agent)was varied as shown in Table 4.

For the positive electrode material mixture C_(1n), 5 parts by weight ofgraphite (conductive agent) was added per 100 parts by weight of thetotal of the nickel oxyhydroxide C₁ and manganese dioxide, and zincoxide was further added thereto in an amount corresponding to 5 wt % ofthe nickel oxyhydroxide C₁. Furthermore, 1 part by weight of theelectrolyte was added per 100 parts by weight of the total of the nickeloxyhydroxide C₁ and manganese dioxide. Thereafter, the mixture washomogeneously stirred and mixed in a mixer, and then formed intoparticulates with a predetermined particle size. The resultingparticulates were pressure-molded into a pellet in the shape of a shortcylinder, thereby producing a positive electrode material mixturepellet. An AA-sized nickel-manganese battery C_(1n) was fabricated inthe same manner as in Example 1, except for using this positiveelectrode material mixture pellet.

AA-sized nickel-manganese batteries C_(2n) to C_(6n) were fabricated ina manner similar to that described above, using the nickel oxyhydroxidesC₂ to C₆ in place of the nickel oxyhydroxide C₁. At this time, it wasmade sure that the amount of the positive electrode material mixturefilled in the positive electrode case was the same for all thebatteries. TABLE 4 Content of manganese dioxide in positive electrodematerial mixture Nickel oxyhydroxide (wt %) C₁ C₂ C₃ C₄ C₅ C₆ 10Positive electrode Positive electrode Positive electrode Positiveelectrode Positive electrode Positive electrode material mixture C₁₁material mixture C₂₁ material mixture C₃₁ material mixture C₄₁ materialmixture C₅₁ material mixture C₆₁ 20 Positive electrode Positiveelectrode Positive electrode Positive electrode Positive electrodePositive electrode material mixture C₁₂ material mixture C₂₂ materialmixture C₃₂ material mixture C₄₂ material mixture C₅₂ material mixtureC₆₂ 30 Positive electrode Positive electrode Positive electrode Positiveelectrode Positive electrode Positive electrode material mixture C₁₃material mixture C₂₃ material mixture C₃₃ material mixture C₄₃ materialmixture C₅₃ material mixture C₆₃ 40 Positive electrode Positiveelectrode Positive electrode Positive electrode Positive electrodePositive electrode material mixture C₁₄ material mixture C₂₄ materialmixture C₃₄ material mixture C₄₄ material mixture C₅₄ material mixtureC₆₄ 60 Positive electrode Positive electrode Positive electrode Positiveelectrode Positive electrode Positive electrode material mixture C₁₅material mixture C₂₅ material mixture C₃₅ material mixture C₄₅ materialmixture C₅₅ material mixture C₆₅ 80 Positive electrode Positiveelectrode Positive electrode Positive electrode Positive electrodePositive electrode material mixture C₁₆ material mixture C₂₆ materialmixture C₃₆ material mixture C₄₆ material mixture material mixture C₆₆C₅₆ 90 Positive electrode Positive electrode Positive electrode Positiveelectrode Positive electrode Positive electrode material mixture C₁₇material mixture C₂₇ material mixture C₃₇ material mixture C₄₇ materialmixture C₅₇ material mixture C₆₇ 95 Positive electrode Positiveelectrode Positive electrode Positive electrode Positive electrodePositive electrode material mixture C₁₈ material mixture C₂₈ materialmixture C₃₈ material mixture material mixture C₅₈ material mixture C₆₈C₄₈[4] Evaluation of Alkaline Batteries

Each of the thus fabricated 48 types of nickel-manganese batteriesC_(1n) to C_(6n), and the battery A (using β-nickel oxyhydroxide), whichwas fabricated in Example 1, were continuously discharged at 20° C. witha constant current of 50 mA, and the discharge capacity obtained duringa period in which the battery voltage reached 0.9 V was measured.

In addition, each of the batteries in the initial state was continuouslydischarged at 20° C. with a constant power of 1 W, and the dischargecapacity obtained during a period in which the battery voltage reached0.9 V was also measured.

The results obtained were summarized in Table 5. It should be noted thatin both the 50 mA discharge and the 1 W discharge, the dischargecapacity of each of the nickel-manganese batteries B to D was shown as arelative value, taking the discharge capacity of the nickel-manganesebattery A as 100. TABLE 5 Content of 50 mA 1 W manganese dis- dis-dioxide charge charge Battery Nickel oxyhydroxide (wt %) capacitycapacity Battery A1 Nickel oxyhydroxide A 50 100 100 Battery C₁₁ Nickeloxyhydroxide C₁ 10 102 102 Battery C₁₂ Nickel oxyhydroxide C₁ 20 105 102Battery C₁₃ Nickel oxyhydroxide C₁ 30 110 103 Battery C₁₄ Nickeloxyhydroxide C₁ 40 111 103 Battery C₁₅ Nickel oxyhydroxide C₁ 60 111 103Battery C₁₆ Nickel oxyhydroxide C₁ 80 112 102 Battery C₁₇ Nickeloxyhydroxide C₁ 90 112 102 Battery C₁₈ Nickel oxyhydroxide C₁ 95 112 101Battery C₂₁ Nickel oxyhydroxide C₂ 10 102 102 Battery C₂₂ Nickeloxyhydroxide C₂ 20 107 105 Battery C₂₃ Nickel oxyhydroxide C₂ 30 113 108Battery C₂₄ Nickel oxyhydroxide C₂ 40 112 108 Battery C₂₅ Nickeloxyhydroxide C₂ 60 112 107 Battery C₂₆ Nickel oxyhydroxide C₂ 80 113 106Battery C₂₇ Nickel oxyhydroxide C₂ 90 113 103 Battery C₂₈ Nickeloxyhydroxide C₂ 95 114 102 Battery C₃₁ Nickel oxyhydroxide C₃ 10 105 102Battery C₃₂ Nickel oxyhydroxide C₃ 20 111 111 Battery C₃₃ Nickeloxyhydroxide C₃ 30 114 114 Battery C₃₄ Nickel oxyhydroxide C₃ 40 114 115Battery C₃₅ Nickel oxyhydroxide C₃ 60 115 114 Battery C₃₆ Nickeloxyhydroxide C₃ 80 114 113 Battery C₃₇ Nickel oxyhydroxide C₃ 90 114 111Battery C₃₈ Nickel oxyhydroxide C₃ 95 115 103 Battery C₄₁ Nickeloxyhydroxide C₄ 10 105 104 Battery C₄₂ Nickel oxyhydroxide C₄ 20 111 111Battery C₄₃ Nickel oxyhydroxide C₄ 30 114 116 Battery C₄₄ Nickeloxyhydroxide C₄ 40 116 117 Battery C₄₅ Nickel oxyhydroxide C₄ 60 115 116Battery C₄₆ Nickel oxyhydroxide C₄ 80 116 115 Battery C₄₇ Nickeloxyhydroxide C₄ 90 116 111 Battery C₄₈ Nickel oxyhydroxide C₄ 95 117 103Battery C₅₁ Nickel oxyhydroxide C₅ 10 104 104 Battery C₅₂ Nickeloxyhydroxide C₅ 20 112 112 Battery C₅₃ Nickel oxyhydroxide C₅ 30 115 116Battery C₅₄ Nickel oxyhydroxide C₅ 40 120 119 Battery C₅₅ Nickeloxyhydroxide C₅ 60 119 118 Battery C₅₆ Nickel oxyhydroxide C₅ 80 120 115Battery C₅₇ Nickel oxyhydroxide C₅ 90 120 112 Battery C₅₈ Nickeloxyhydroxide C₅ 95 119 103 Battery C₆₁ Nickel oxyhydroxide C₆ 10 108 105Battery C₆₂ Nickel oxyhydroxide C₆ 20 115 110 Battery C₆₃ Nickeloxyhydroxide C₆ 30 124 115 Battery C₆₄ Nickel oxyhydroxide C₆ 40 124 117Battery C₆₅ Nickel oxyhydroxide C₆ 60 123 116 Battery C₆₆ Nickeloxyhydroxide C₆ 80 124 114 Battery C₆₇ Nickel oxyhydroxide C₆ 90 124 110Battery C₆₈ Nickel oxyhydroxide C₆ 95 120 104

From Table 5, the following can be stated:

First, in the cases of the alkaline batteries C₁₁ to C₆₈, which usednickel oxyhydroxide in which manganese and cobalt were dissolved, theaverage valence of nickel was increased by the presence of manganese,and moreover, the electron conductivity was improved by the presence ofcobalt. Accordingly, each of the batteries C₁₁ to C₆₈ provided enhancedcharacteristics, as compared with those of the battery A1, which usedβ-nickel oxyhydroxide.

In particular, the batteries C₃₂ to C₃₇, C₄₂ to C₄₇, C₅₂ to C₅₇ and C₆₂to C₆₇, which used nickel oxyhydroxides (C₃ to C₆) having a value ofI_(γ)/(I_(γ)+I_(β)) of not less than 0.5 and an average valence ofnickel of not less than 3.3 and in which the content of the manganesedioxide in the positive electrode material mixture was 20 to 90 wt %,had exhibited a significant improvement in the 1 W (heavy load)discharge as compared with the battery A, and provided characteristicsas high as 110 or above in Table 5.

The reason that the above-described results were obtained seems to be asfollows:

First, when the contents of manganese dioxide are the same, the higherthe production ratio of the γ-type crystal structure

I_(γ)/(I_(γ)+I_(β))value

or the average valence of nickel in the nickel oxyhydroxide (i.e., inthe order from C₁ to C₆), the higher the capacity becomes, since themultiple-electron reaction of nickel can be utilized for discharge.

On the other hand, manganese dioxide has a large capacity, but has poorin electron conductivity and hence low efficiency during discharge underheavy load, and therefore, the 1 W characteristics start to decreasewhen the content of manganese dioxide exceeds 90 wt %.

Further, it is inferred that when the content of manganese dioxide is asextremely low as 10 wt %, it becomes difficult to establish a successfulconnection between the active materials with graphite due to a decreasein moldability of the positive electrode material mixture pellet, thusalso decreasing the 1 W characteristics.

It seems that, for the reasons as described above, the batteries thatused particles comprising nickel oxyhydroxide with a value ofI_(γ)/(I_(γ)+I_(β)) of not less than 0.5 and an average valence ofnickel of not less than 3.3 and in which the content of the manganesedioxide in the positive electrode material mixture was 20 to 90 wt %provided particularly excellent characteristics.

In addition, although not described in details here, characteristicsthat were generally higher than those of the battery A1 using β-nickeloxyhydroxide could also be achieved when using the nickel oxyhydroxideD1, which was used in Example 1. Particularly, another test confirmed asignificant improvement in the performance, mainly the heavy loadcharacteristics, of the alkaline batteries could be achieve when theparticles comprising nickel oxyhydroxide with a value ofI_(γ)/(I_(γ)+I_(β)) of not less than 0.5 and an average valence ofnickel of not less than 3.3 were coated with a cobalt oxide and thecontent of the manganese dioxide in the positive electrode materialmixture was 20 to 90 wt %.

EXAMPLE 3

In order to optimize the amounts of manganese and cobalt dissolved inthe particles comprising nickel oxyhydroxide, the following tests andevaluations were performed.

[1] Production of Particles Comprising Nickel Hydroxide

Pure water and a small amount of hydrazine (reducing agent) were addedinto a reaction vessel provided with a stirring blade, and bubbling witha nitrogen gas was started. Additionally, a nickel (II) sulfate aqueoussolution, a manganese (II) sulfate aqueous solution, a cobalt (II)sulfate aqueous solution, a sodium hydroxide aqueous solution andammonia water having predetermined concentrations were prepared. Theywere supplied with pumps into the above-described reaction vessel suchthat the pH in the vessel was constant, and continuous stirring wasperformed sufficiently, thereby precipitating and growing a solidsolution comprising spherical β-nickel hydroxide in which manganese andcobalt were dissolved.

Subsequently, the resulting particles were heated in a sodium hydroxideaqueous solution that was different from the one described above toremove sulfate ions, followed by washing with water and vacuum drying,and they were further subjected to air oxidation at 80° C. for 72 hours,thereby producing a nickel hydroxide aa

composition: Ni_(0.99)Mn_(0.005)Co_(0.005)(OH)₂

. Here, the air oxidation was a treatment for oxidizing only Mn to avalence near 4.

Further, nickel hydroxides ab to ay having the compositions as shown inTable 6 were synthesized in the same manner as described above, exceptfor varying the ratios of the manganese (II) sulfate aqueous solutionand the cobalt (II) sulfate aqueous solution that were supplied into thereaction vessel.

[2] Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

After 200 g of the nickel hydroxide aa was introduced into 1 L of a 5mol/L sodium hydroxide aqueous solution, a sufficient amount of a sodiumhypochlorite aqueous solution (effective chlorine concentration: 5 wt %)serving as an oxidizing agent was added thereto, and the whole wasstirred to convert the nickel hydroxide to nickel oxyhydroxide. Theresulting particles were sufficiently washed with water, followed byvacuum drying at 60° C. (24 hours), thereby producing a nickeloxyhydroxide AA.

Additionally, nickel oxyhydroxides AB to AY were procuded by performinga process similar to that described above, using the nickel hydroxidesab to ay, respectively, in place of the nickel hydroxide aa.

[3] Analysis of Physical Properties of Nickel Oxyhydroxides

Table 6 summarizes the values of I_(γ)/(I_(γ)+I_(β)) obtained by powderX-ray diffraction and the average valence of nickel obtained by achemical analysis for the resulting 25 different nickel oxyhydroxides C₁to C₆.

From Table 6, it can be seen that in the case of the nickeloxyhydroxides AA to AE, in which the amount of manganese dissolved wasas extremely low as 0.5 mol % (Mn_(0.005)), the production ratio of theγ-type crystal structure and the average valence of nickel were lowerthan those of the rest. TABLE 6 I_(γ)/ Average (I_(γ) + valence Nickelhydroxide I_(β)) of Nickel oxyhydroxide source material value nickelNickel oxyhydroxide AA Nickel hydroxide aa: 0.23 3.15Ni_(0.99)Mn_(0.005)Co_(0.005)(OH)₂ Nickel oxyhydroxide AB Nickelhydroxide ab: 0.24 3.16 Ni_(0.985)Mn_(0.005).Co_(0.01)(OH)₂ Nickeloxyhydroxide AC Nickel hydroxide ac: 0.25 3.18_(Ni0.945)Mn_(0.005)Co_(0.05)(OH)₂ Nickel oxyhydroxide AD Nickelhydroxide ad: 0.28 3.18 Ni_(0.925)Mn_(0.005)Co_(0.07)(OH)₂ Nickeloxyhydroxide AE Nickel hydroxide ae: 0.29 3.19Ni_(0.895)Mn_(0.005)Co_(0.10)(OH)₂ Nickel oxyhydroxide AF Nickelhydroxide af: 0.53 3.32 Ni_(0.985)Mn_(0.01)Co_(0.005)(OH)₂ Nickeloxyhydroxide AG Nickel hydroxide ag: 0.55 3.34Ni_(0.98)Mn_(0.01)Co_(0.01)(OH)₂ Nickel oxyhydroxide AH Nickel hydroxideah: 0.56 3.35 Ni_(0.94)Mn_(0.01)Co_(0.05)(OH)₂ Nickel oxyhydroxide AINickel hydroxide ai: 0.55 3.35 Ni_(0.92)Mn_(0.01)Co_(0.07)(OH)₂ Nickeloxyhydroxide AJ Nickel hydroxide aj: 0.57 3.34Ni_(0.89)Mn_(0.01)Co_(0.10)(OH)₂ Nickel oxyhydroxide AK Nickel hydroxideak: 0.80 3.40 Ni_(0.945)Mn_(0.05)Co_(0.005)(OH)₂ Nickel oxyhydroxide ALNickel hydroxide al: 0.80 3.39 Ni_(0.94)Mn_(0.05)Co_(0.01)(OH)₂ Nickeloxyhydroxide AM Nickel hydroxide am: 0.81 3.40Ni_(0.90)Mn_(0.05)Co_(0.05)(OH)₂ Nickel oxyhydroxide AN Nickel hydroxidean: 0.82 3.40 Ni_(0.88)Mn_(0.05)Co_(0.07)(OH)₂ Nickel oxyhydroxide AONickel hydroxide ao: 0.81 3.41 Ni_(0.85)Mn_(0.05)Co_(0.10)(OH)₂ Nickeloxyhydroxide AP Nickel hydroxide ap: 0.84 3.44Ni_(0.925)Mn_(0.07)Co_(0.005)(OH)₂ Nickel oxyhydroxide AQ Nickelhydroxide aq: 0.86 3.46 Ni_(0.92)Mn_(0.07)Co_(0.01)(OH)₂ Nickeloxyhydroxide AR Nickel hydroxide ar: 0.85 3.45Ni_(0.88)Mn_(0.07)Co_(0.05)(OH)₂ Nickel oxyhydroxide AS Nickel hydroxideas: 0.85 3.45 Ni_(0.86)Mn_(0.07)Co_(0.07)(OH)₂ Nickel oxyhydroxide ATNickel hydroxide at: 0.86 3.46 Ni_(0.83)Mn_(0.07)Co_(0.10)(OH)₂ Nickeloxyhydroxide AU Nickel hydroxide au: 0.91 3.50Ni_(0.895)Mn_(0.10)Co_(0.005)(OH)₂ Nickel oxyhydroxide AV Nickelhydroxide av: 0.92 3.51 Ni_(0.89)Mn_(0.10)Co_(0.01)(OH)₂ Nickeloxyhydroxide AW Nickel hydroxide aw: 0.92 3.50Ni_(0.85)Mn_(0.10)Co_(0.05)(OH)₂ Nickel oxyhydroxide AX Nickel hydroxideax: 0.91 3.51 Ni_(0.83)Mn_(0.10)Co_(0.07)(OH)₂ Nickel oxyhydroxide AYNickel hydroxide ay: 0.93 3.52 Ni_(0.80)Mn_(0.10)Co_(0.10)(OH)₂[4] Fabrication of Alkaline Batteries

Nickel-manganese batteries AA to AY serving as primary batteries wereproduced, using the nickel oxyhydroxides AA to AY, respectively.

For the nickel-manganese battery AA, the nickel oxyhydroxide AA,manganese dioxide and graphite were mixed at a weight ratio of 50:50:5,and zinc oxide was further added to this mixture in an amountcorresponding to 5 wt % of the nickel oxyhydroxide AA. Furthermore, 1part by weight of the electrolyte was added per 100 parts by weight ofthe total of the nickel oxyhydroxide AA and manganese dioxide.Thereafter, the mixture was homogeneously stirred and mixed in a mixer,and then formed into particulates with a predetermined particle size.The resulting particulates were pressure-molded into a pellet in theshape of a short cylinder, thereby producing a positive electrodematerial mixture pellet. An AA-sized alkaline battery AA was fabricatedin the same manner as in Example 1, except for using this positiveelectrode material mixture pellet.

AA-sized nickel-manganese batteries AB to AY were fabricated in a mannersimilar to that described above, using the nickel oxyhydroxides AB to AYin place of the nickel oxyhydroxide AA. At this time, it was made surethat the amount of the positive electrode material mixture filled in thepositive electrode case was the same for all the batteries.

[5] Evaluation of Alkaline Batteries

Each of the thus fabricated 25 types of nickel-manganese batteries AB toAY and the battery A (using β-nickel oxyhydroxide), which was fabricatedin Example 1, were continuously discharged at 20° C. with a constantcurrent of 50 mA, and the discharge capacity obtained during a period inwhich the battery voltage reached 0.9 V was measured.

In addition, each of the batteries in the initial state was continuouslydischarged at 20° C. with a constant power of 1 W, and the dischargecapacity obtained during a period in which the battery voltage reached0.9 V was also measured.

The results obtained were summarized in Table 7. It should be noted thatin both the 50 mA discharge and the 1 W discharge, the dischargecapacity of each of the nickel-manganese batteries AA to AY was shown asa relative value, taking the discharge capacity of the nickel-manganesebattery A as 100. TABLE 7 50 mA discharge 1 W discharge Battery Nickeloxyhydroxide capacity capacity Battery A1 Nickel oxyhydroxide A Nickelhydroxide a: 100 100 Ni(OH) Battery AA Nickel oxyhydroxide AA Nickelhydroxide aa: 111 106 Ni_(0.99)Mn_(0.005)Co_(0.005)(OH)₂ Battery ABNickel oxyhydroxide AB Nickel hydroxide ab: 112 107Ni_(0.985)Mn_(0.005).Co_(0.01)(OH)₂ Battery AC Nickel oxyhydroxide ACNickel hydroxide ac: 112 108 Ni_(0.945)Mn_(0.005)Co_(0.05)(OH)₂ BatteryAD Nickel oxyhydroxide AD Nickel hydroxide ad: 112 108Ni_(0.925)Mn_(0.005)Co_(0.07)(OH)₂ Battery AE Nickel oxyhydroxide AENickel hydroxide ae: 112 109 Ni_(0.895)Mn_(0.005)Co_(0.10)(OH)₂ BatteryAF Nickel oxyhydroxide AF Nickel hydroxide af: 115 107Ni_(0.985)Mn_(0.01)Co_(0.005)(OH)₂ Battery AG Nickel oxyhydroxide AGNickel hydroxide ag: 115 112 Ni_(0.98)Mn_(0.01)Co_(0.01)(OH)₂ Battery AHNickel oxyhydroxide AH Nickel hydroxide ah: 116 113Ni_(0.94)Mn_(0.01)Co_(0.05)(OH)₂ Battery AI Nickel oxyhydroxide AINickel hydroxide ai: 115 112 Ni_(0.92)Mn_(0.01)Co_(0.07)(OH)₂ Battery AJNickel oxyhydroxide AJ Nickel hydroxide aj: 113 107Ni_(0.89)Mn_(0.01)Co_(0.10)(OH)₂ Battery AK Nickel oxyhydroxide AKNickel hydroxide ak: 119 106 Ni_(0.945)Mn_(0.05)Co_(0.005)(OH)₂ BatteryAL Nickel oxyhydroxide AL Nickel hydroxide al: 120 113Ni_(0.94)Mn_(0.05)Co_(0.01)(OH)₂ Battery AM Nickel oxyhydroxide AMNickel hydroxide am: 120 117 Ni_(0.90)Mn_(0.05)Co_(0.05)(OH)₂ Battery ANNickel oxyhydroxide AN Nickel hydroxide an: 119 114Ni_(0.88)Mn_(0.05)Co_(0.07)(OH)₂ Battery AO Nickel oxyhydroxide AONickel hydroxide ao: 115 108 Ni_(0.85)Mn_(0.05)Co_(0.10)(OH)₂ Battery APNickel oxyhydroxide AP Nickel hydroxide ap: 120 106Ni_(0.925)Mn_(0.07)Co_(0.005)(OH)₂ Battery AQ Nickel oxyhydroxide AQNickel hydroxide aq: 120 113 Ni_(0.92)Mn_(0.07)Co_(0.01)(OH)₂ Battery ARNickel oxyhydroxide AR Nickel hydroxide ar: 121 116Ni_(0.88)Mn_(0.07)Co_(0.05)(OH)₂ Battery AS Nickel oxyhydroxide ASNickel hydroxide as: 120 114 Ni_(0.86)Mn_(0.07)Co_(0.07)(OH)₂ Battery ATNickel oxyhydroxide AT Nickel hydroxide at: 115 109Ni_(0.83)Mn_(0.07)Co_(0.10)(OH)₂ Battery AU Nickel oxyhydroxide AUNickel hydroxide au: 116 102 Ni_(0.895)Mn_(0.10)Co_(0.005)(OH)₂ BatteryAV Nickel oxyhydroxide AV Nickel hydroxide av: 115 106Ni_(0.89)Mn_(0.10)Co_(0.01)(OH)₂ Battery AW Nickel oxyhydroxide AWNickel hydroxide aw: 114 108 Ni_(0.85)Mn_(0.10)Co_(0.05)(OH)₂ Battery AXNickel oxyhydroxide AX Nickel hydroxide ax: 113 107Ni_(0.83)Mn_(0.10)Co_(0.07)(OH)₂ Battery AY Nickel oxyhydroxide AYNickel hydroxide ay: 111 103 Ni_(0.80)Mn_(0.10)Co_(0.10)(OH)₂

From Table 7, the following can be stated.

First, in the cases of the alkaline batteries AA to AY, which usednickel oxyhydroxide in which manganese and cobalt were dissolved, theaverage valence of nickel was increased by the presence of manganese,and moreover, the electron conductivity was improved by the presence ofcobalt. Accordingly, each of the batteries AA to AY provided enhancedcharacteristics, as compared with the battery A1, which used β-nickeloxyhydroxide.

In particular, the cases in which the amounts of manganese and cobaltdissolved in the nickel oxyhydroxide were 1 to 7 mol % of the total ofthe metallic elements included in the particles comprising the nickeloxyhydroxide, that is, the batteries using the nickel oxyhydroxides AGto AI, AL to AN and AQ to AS exhibited a significant capacity increasein both the 50 mA (low load) discharge and the 1 W (heavy load)discharge, and provided characteristics as high as 110 or above in Table7.

As is evident from the results in Table 6, the batteries AA to AE, inwhich the amount of manganese dissolved in the nickel oxyhydroxide wasless than 1 mol %, could not provide nickel oxyhydroxide having a highdegree of oxidation, and thus exhibited a relatively small capacityincrease. On the other hand, the batteries AU to AY, in which the amountof manganese dissolved in the nickel oxyhydroxide was greater than 7 mol%, had a relatively small content of nickel in the nickel oxyhydroxides,and was affected by reduced electron conductivity, which is typical of asolid solution containing manganese, during the heavy load discharge, sothat they tended to decrease in capacity.

Furthermore, the batteries AA, AF, AK, AP and AU, in which the amount ofcobalt dissolved in the nickel oxyhydroxide was less than 1 mol %,showed a relatively small effect of the addition of cobalt on improvingthe electron conductivity and the proton diffusion. On the other hand,the batteries AE, AJ, AO, AT and AY, in which the amount of cobaltdissolved in the nickel oxyhydroxide was greater than 7 mol %, had arelatively small content of nickel in the nickel oxyhydroxide, andtherefore had a relatively small capacity increase.

Thus, from the viewpoint of increasing the capacity, it is particularlypreferable in the present invention that the amount of each of manganeseand cobalt dissolved in particles comprising nickel oxyhydroxide ornickel hydroxide serving as a source material thereof is 1 to 7 mol % ofthe total of the metallic elements included in the particles.

EXAMPLE 4

In order to optimize the amount of cobalt oxide attached onto thesurface of the particles comprising nickel oxyhydroxide, the followingtests and evaluations were performed.

[1] Production of Particles Comprising Nickel Oxyhydroxide

After the nickel hydroxide b1

composition: Ni_(0.95)Mn₀₀₅(OH)₂

, used in Example 1, was introduced into a cobalt sulfate aqueoussolution in a reaction vessel, a sodium hydroxide aqueous solution wasgradually added thereto, and the whole was continuously stirred at 35°C. while adjusting the pH in the vessel such that it was maintained at10, thus precipitating cobalt hydroxide on the surface of the solidsolution particles.

At this time, the amount of cobalt hydroxide attached onto the surfaceof the nickel hydroxide b was varied in the range from 0.05 to 9 partsby weight per 100 parts by weight of the nickel hydroxide b1 (0.05 to 9wt % relative to the nickel hydroxide b) by appropriately adjusting theconcentration of the cobalt sulfate aqueous solution. Thus, seven typesof nickel hydroxides e1 to k1 as shown in Table 8, which were coatedwith Co(OH)₂, were produced. The nickel hydroxides e1 to k1 were washedwith water, and thereafter vacuum dried.

[2] Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

After 200 g of the nickel hydroxide e1 was introduced into 1 L of a 5mol/L sodium hydroxide aqueous solution, a sufficient amount of a sodiumhypochlorite aqueous solution (effective chlorine concentration: 5 wt %)serving as an oxidizing agent was added thereto, and the whole wasstirred to convert the nickel hydroxide to nickel oxyhydroxide, whileoxidizing Co(OH)₂. The resulting particles were sufficiently washed withwater, followed by vacuum drying at 60° C. (24 hours), thereby producinga nickel oxyhydroxide E1.

Additionally, nickel oxyhydroxides F1 to K1 were produced by performinga process similar to that described above, using the nickel hydroxidesf1 to k1, respectively, in place of the nickel hydroxide e1. TABLE 8Co(OH)₂-coated Nickel Amount of hydroxide Co (OH)₂ (wt %) Nickelhydroxide e1 0.05 Nickel hydroxide f1 0.1 Nickel hydroxide g1 1 Nickelhydroxide h1 3 Nickel hydroxide I1 5 Nickel hydroxide j1 7 Nickelhydroxide k1 9[3] Fabrication of Alkaline Batteries

Nickel-manganese batteries E1 to K1 serving as primary batteries wereproduced, using the nickel oxyhydroxides E1 to K1, respectively.

For the nickel-manganese battery E1, the nickel oxyhydroxide E1,manganese dioxide and graphite were mixed at a weight ratio of 50:50:5,and zinc oxide was further added to this mixture in an amountcorresponding to 5 wt % of the nickel oxyhydroxide E1. Furthermore, 1part by weight of the alkaline electrolyte was added per 100 parts byweight of the total of the nickel oxyhydroxide E1 and manganese dioxide.Thereafter, the mixture was homogeneously stirred and mixed in a mixer,and then formed into particulates with a predetermined particle size.The resulting particulates were molded into a pellet in the shape of ashort cylinder, thereby producing a positive electrode material mixturepellet. An AA-sized alkaline battery E1 was fabricated in the samemanner as in Example 1, except for using this positive electrodematerial mixture pellet.

Further, AA-sized nickel-manganese batteries F1 to K1 were fabricated ina manner similar to that described above, using the nickel oxyhydroxidesF1 to K1 in place of the nickel oxyhydroxide E1. At this time, it wasmade sure that the amount of the positive electrode material mixturefilled in the positive electrode case was the same for all thebatteries.

[4] Evaluation of Alkaline Batteries

Each of the thus fabricated 7 types of nickel-manganese batteries E1 toK1, and the battery A1 (using β-nickel oxyhydroxide) fabricated inExample 1, were continuously discharged at 20° C. with a constantcurrent of 50 mA, and the discharge capacity obtained during a period inwhich the battery voltage reached 0.9 V was measured.

In addition, each of the batteries in the initial state was continuouslydischarged at 20° C. with a constant power of 1 W, and the dischargecapacity obtained during a period in which the battery voltage reached0.9 V was also measured.

Here, each of the batteries that had undergone the 1 W discharge wasfurther stored at 60° C. for seven days, and then the amount of gasgenerated inside the battery was measured.

The results obtained were summarized in Table 9. It should be noted thatin both the 50 mA discharge and the 1 W discharge, the dischargecapacity of each of the nickel-manganese batteries E1 to K1 and theamount of gas generated inside each of the batteries E1 to K1 afterdischarge were shown as relative values, taking the discharge capacityof and the amount of gas generated in the nickel-manganese battery A1 as100. TABLE 9 Element Amount of 50 mA 1 W Amount of gas Nickel containedin Co oxide discharge discharge generated Battery oxyhydroxide solidsolution (wt %) capacity capacity during storage Battery A1 Nickel — 0100 100 100 oxyhydroxide A1 Battery E1 Nickel Mn 5 mol % 0.05 119 105100 oxyhydroxide E1 Battery F1 Nickel Mn 5 mol % 0.1 120 111 100oxyhydroxide F1 Battery G1 Nickel Mn 5 mol % 1 120 114 101 oxyhydroxideG1 Battery H1 Nickel Mn 5 mol % 3 121 115 101 oxyhydroxide H1 Battery I1Nickel Mn 5 mol % 5 121 116 102 oxyhydroxide I1 Battery J1 Nickel Mn 5mol % 7 120 113 103 oxyhydroxide J1 Battery K1 Nickel Mn 5 mol % 9 118109 111 oxyhydroxide K1

From Table 9, the following can be stated.

First, in the cases of the alkaline batteries E1 to K1, which usedparticles comprising nickel oxyhydroxide and having a cobalt oxideattached onto its surface, the average valence of nickel was increasedby the presence of manganese dissolved in the particles comprising thenickel oxyhydroxide, and moreover, the electrical connection between theactive materials was improved by the cobalt oxide. Accordingly, each ofthe batteries E1 to K1 provided enhanced characteristics, as comparedwith the battery A1, which used particles comprising β-nickeloxyhydroxide.

In particular, the batteries F1 to J1, in which the weight percentage ofthe cobalt oxide relative to the particles comprising the nickeloxyhydroxide was 0.1 to 7 wt %, achieved a high discharge capacity bothin the 50 mA (low load) discharge and the 1 W (heavy load) discharge,and provided characteristics as high as 110 or above in Table 9.Furthermore, the amount of gas generated during storage was suppressedto the same level as that of the battery A.

The battery E1 using the nickel oxyhydroxide E1, in which the weightpercentage of the cobalt oxide was less than 0.1 wt %, had anexcessively small amount of the cobalt oxide, and therefore had not yetachieved a significant improving effect for the heavy load dischargecharacteristics.

The battery K using the nickel oxyhydroxide K1, in which the weightpercentage of the cobalt oxide was greater than 7 wt %, could maintainrelatively favorable discharge characteristics, but had an increasedamount of gas generated when the discharged battery was stored at 60° C.for seven days. The reason for this seems to be that the battery K1 hadan excessive amount of the cobalt oxide in the positive electrode, sothat the cobalt oxide in the positive electrode was reduced to a valenceof 2 and dissolved into the electrolyte, when the discharged battery wasstood still (stored). It is inferred that the cobalt ions thenprecipitated as metallic cobalt on the zinc particles of the negativeelectrode, thus accelerating the hydrogen generation reaction in thenegative electrode.

As described above, in the case of coating the surface of particlescomprising nickel oxyhydroxide with a cobalt oxide, it is preferablethat the amount of the cobalt oxide is 0.1 to 7 wt % of the particlescomprising the nickel oxyhydroxide, from the viewpoint of securing asuitable balance between the discharge characteristics and the storagecharacteristics (reliability).

Here, in this example, a solid solution nickel hydroxide

Ni_(0.95)Mn_(0.05)(OH)₂

containing 5 mol % of Mn was used as the source material for particlescomprising nickel oxyhydroxide. However, in view of the results ofExample 3, for example, it is inferred that similar batterycharacteristics can be obtained when the amount of dissolved Mncontained in the solid solution was in the range of 1 to 7 mol %.

EXAMPLE 5

[1] Production of Nickel Hydroxide

A nickel (II) sulfate aqueous solution, a sodium hydroxide aqueoussolution and ammonia water having predetermined concentrations wereprepared, and they were supplied with pumps into a reaction vesselprovided with a stirring blade such that the pH in the vessel wasconstant, and continuous stirring was performed sufficiently, therebyprecipitating and growing spherical β-nickel hydroxide.

Subsequently, the resulting particles were heated in a sodium hydroxideaqueous solution that was different from the one described above toremove sulfate ions, followed by washing with water and drying, therebyproducing a nickel hydroxide powder. The average particle diameter on avolume basis of the resulting nickel hydroxide powder measured by alaser diffraction particle size distribution analyzer was 10 μm, and theBET specific surface area was 9.0 m²/g, and the tap density was 2.20g/cm³.

[2] Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

Next, as the oxidation treatment for the nickel hydroxide powder, twotreatments, namely, a chemical oxidation treatment using an oxidizingagent and an overoxidation treatment (overcharge treatment) using anelectrochemical reaction were investigated.

(1) Chemical Oxidation Treatment Using Oxidizing Agent

<1> Nickel Oxyhydroxide a2

After 200 g of the nickel hydroxide powder was introduced into 1 L of a0.5 mol/L sodium hydroxide aqueous solution, a sufficient amount of asodium hypochlorite aqueous solution (effective chlorine concentration:5 wt %) serving as an oxidizing agent was added thereto, and the wholewas stirred to convert the nickel hydroxide into nickel oxyhydroxide.The resulting particles were sufficiently washed with water, followed byvacuum drying at 60° C. (24 hours), thereby producing a nickeloxyhydroxide a2.

<2> Nickel Oxyhydroxide b2

A nickel oxyhydroxide b2 was produced by performing the same chemicaloxidation treatment as described in <1> above, except for using a sodiumhydroxide aqueous solution having a high concentration of 7 mol/L inplace of the 0.5 mol/L sodium hydroxide aqueous solution.

(2) Overoxidation Treatment Using Electrochemical Reaction

<1> Nickel Oxyhydroxide c2

A suitable amount of pure water was added to the nickel oxyhydroxide a2to form a paste, and a predetermined amount of this was filled in afoamed nickel substrate having a porosity of 95%. Subsequently, thenickel substrate in which the paste was filled was dried in a dryer at80° C., then rolled with a roll press, and a nickel lead for currentcollection was attached onto the nickel substrate, thus forming a nickelpositive electrode. An open-type cell was fabricated using this nickelpositive electrode, a cadmium oxide negative electrode having asufficiently large capacity, a nonwoven fabric separator made ofpolypropylene that had been subjected to a hydrophilization treatmentand a 7 mol/L sodium hydroxide aqueous solution.

In the open-type cell, an overcharge (overoxidation) treatment wasperformed on the positive electrode. At this time, the electricalcapacity obtained assuming that the nickel oxyhydroxide a2 filled in thepositive electrode underwent one-electron reaction was taken as the cellcapacity (1 It), and overcharge was performed at a charge rate of 0.1 Itfor three hours. After the overcharge, the nickel positive electrode wascollected, and then subjected to ultrasonic cleaning to collect thenickel oxyhydroxide, which was then washed with water. Thereafter,vacuum drying was performed at 60° C. (24 hours), thereby obtaining anickel oxyhydroxide c2 that had been subjected to a overchargetreatment.

<2> Nickel Oxyhydroxides d2, e2, f2

Nickel oxyhydroxide d2, e2 and f2 were obtained by performing the sameovercharge treatment as described in <1> above, except that charging wascarried out at a charge rate of 0.1 It for 6 hours, 9 hours and 12hours, respectively.

[3] Analysis of Physical Properties of Nickel Oxyhydroxides

First, powder X-ray diffraction was performed on the nickeloxyhydroxides a2 to f2. As a result, the presence of nickel oxyhydroxidewas confirmed in all of the diffraction patterns. The nickeloxyhydroxide f2 was substantially a single phase of γ-nickeloxyhydroxide, and its peak pattern coincided with the JCPDS inorganicmaterial file, File No. 6-75. On the other hand, each of the nickeloxyhydroxides b2 to e2 were a eutectic material of a γ-type crystal anda β-type crystal. FIG. 2 shows the diffraction patterns of the nickeloxyhydroxides e2 and f2 as typical examples.

Table 10 shows the values of I_(γ)/(I_(γ)+I_(β)), the contents ofnickel, the average valences of nickel, the tap densities, the contentsof water, the average particle diameters, the BET specific surface areasthat were obtained for the nickel oxyhydroxides a2 to f2. TABLE 10Average Powder X-ray Nickel Average Tap Water particle BET specific Typeof nickel diffraction content valence of density content diametersurface area oxyhydroxide I_(γ)/(I_(γ) + I_(β)) [wt %] nickel [g/cm³][wt %] [

m] [m²/g] Nickel oxyhydroxide a2 0.01 62.2 3.03 2.30 0.55 10.1 11.0Nickel oxyhydroxide b2 0.07 61.5 3.07 2.27 0.95 11.3 12.4 Nickeloxyhydroxide c2 0.24 58.8 3.22 2.10 1.20 12.2 13.9 Nickel oxyhydroxided2 0.52 56.2 3.36 1.96 1.50 11.7 16.2 Nickel oxyhydroxide e2 0.79 54.83.51 1.85 1.85 11.2 17.8 Nickel oxyhydroxide f2 1.00 53.6 3.62 1.76 2.059.4 19.0

In the cases of the nickel oxyhydroxides a2 and b2, which were obtainedby chemical oxidation, the value of I_(γ)/(I_(γ)+I_(β)) was small andthe average valence of nickel was substantially near 3; however, in thecases of the nickel oxyhydroxides c2 to f2, which were obtained bysubjecting the above-mentioned nickel oxyhydroxides to an overchargetreatment, it was observed that the value of I_(γ)/(I_(γ)+I_(β)) and theaverage valence of nickel effectively increased in accordance with theamount of the charged current capacity. Furthermore, since the expansionand the cracking of the nickel hydroxide particles proceeded with theformation of γ-NiOOH, there was a tendency for the content of nickel andthe tap density to decrease, and for the content of water and the BETspecific surface area to increase.

[4] Fabrication of Alkaline Batteries

Nickel-manganese batteries A2 to F2 as shown in FIG. 1 were fabricatedin a manner similar to that in Example 1, using the nickel oxyhydroxidesa2 to f2, respectively. It should be noted that although the batteriesusing the nickel oxyhydroxides c2 to f2 showed a minor decrease in thefilled amount of the positive electrode material mixture in thebatteries, it was possible to fabricate the batteries basically the sameas those using the nickel oxyhydroxides a2 and b2. The decrease in thefilled amount was attributed to the volume expansion of the powder dueto the formation of γ-NiOOH.

[5] Evaluation of Alkaline Batteries

Each of the batteries A2 to F2 was continuously discharged at 20° C.with a constant current of 50 mA, and the discharge capacity obtainedduring a period in which the battery voltage reached an end voltage of0.9 V was measured. The results obtained were summarized in Table 11. Itshould be noted that, in Table 11, the values of the discharge capacitywere shown as relative values, taking the discharge capacity of thenickel-manganese battery A2 as 100. TABLE 11 Type of Type of nickelBattery capacity battery oxyhydroxide (standardized value) Battery A2Nickel oxyhydroxide a2 100 Battery B2 Nickel oxyhydroxide b2  99 BatteryC2 Nickel oxyhydroxide c2 103 Battery D2 Nickel oxyhydroxide d2 109Battery E2 Nickel oxyhydroxide e2 111 Battery F2 Nickel oxyhydroxide f2114

The batteries C2 to F2, which used nickel oxyhydroxide whose γ-NiOOHcontent had been increased by an overcharge treatment, provided a highercapacity than the batteries A2 and B2, which used nickel oxyhydroxidethat had been obtained by chemical oxidation. In particular, thebatteries using the nickel oxyhydroxides d2 to f2, in which the value ofI_(γ)/(I_(γ)+I_(β)) in a powder X-ray diffraction was increased to notless than 0.5, and the average valence of nickel to not less than 3.3,achieved an even more significant effect of increasing the capacity.

The γ-NiOOH that was produced at a stage where the average valence ofnickel was a relatively small, such as the nickel oxyhydroxide b2 andc2, seems to have made little contribution to the discharge capacity. Onthe other hand, the γ-NiOOH that was produced at a stage where theaverage valence of nickel was not less than about 3.3, such as thenickel oxyhydroxides d2 to f2, seems to have provided a large capacitycorresponding to that valence. The fact that the nickel oxyhydroxides d2to f2 had a relatively large specific surface area and a large effectivearea for electrochemical reaction seems to be a cause of the capacityincrease. However, in the case of producing nickel oxyhydroxide composedmainly of a γ-type crystal by electrochemically overoxidizing(performing overcharge treatment on) β-NiOOH that has been obtained bychemical oxidation, the productivity of the battery becomes relativelylow.

EXAMPLE 6

In order to facilitate the formation of a γ-type crystal, various nickelhydroxides in which Mn as an additive element was dissolved wereproduced as a source material nickel hydroxide, and an attempt was madeto produce nickel oxyhydroxide composed mainly of a γ-type crystal onlyby chemical oxidation. It should be noted that, in all of Synthesis 1 toSynthesis 5 below, the composition of the source material nickelhydroxide was adjusted to Ni_(0.9)Mn_(0.1)(OH)₂.

[1] Synthesis 1

(1) Production of Nickel Hydroxide

Pure water and a small amount of hydrazine (reducing agent) were addedinto a reaction vessel provided with a stirring blade, and bubbling witha nitrogen gas was started. A nickel (II) sulfate aqueous solution, amanganese (II) sulfate aqueous solution, a sodium hydroxide aqueoussolution and ammonia water having predetermined concentrations weresupplied with pumps into the reaction vessel such that the pH in thevessel was constant, and continuous stirring was performed sufficiently,thereby precipitating and growing a solid solution β-nickel hydroxide inwhich Mn was dissolved.

Subsequently, the resulting particles were heated in a sodium hydroxideaqueous solution that was different from the one described above toremove sulfate ions, followed by washing with water and vacuum drying.The dried particles were further subjected to air oxidation at 80° C.for 72 hours to oxidize only manganese, thereby producing a sourcematerial nickel hydroxide 1.

The source material nickel hydroxide 1 was a single phase of β-nickelhydroxide in a powder X-ray diffraction, and had an average valence ofmanganese of 3.95, an average particle diameter of 14 μm, a tap densityof 2.12 g/cm³ and a BET specific surface area of 9.5 m²/g.

(2) Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

Subsequently, after 200 g of the source material nickel hydroxide 1 wasintroduced into 1 L of a 0.5 mol/L sodium hydroxide aqueous solution, asufficient amount of a sodium hypochlorite aqueous solution (effectivechlorine concentration: 5 wt %) serving as an oxidizing agent was addedthereto, and the whole was stirred to convert the nickel hydroxide intonickel oxyhydroxide. The resulting particles were sufficiently washedwith water, followed by vacuum drying at 60° C. (24 hours), therebyproducing a nickel oxyhydroxide g2.

Further, nickel oxyhydroxides h2 to 12 were produced in the same manneras described above, except for changing the concentration of the sodiumhydroxide aqueous solution from 0.5 mol/L to 1 mol/L, 2 mol/L, 3 mol/L,5 mol/L or 7 mol/L.

[2] Synthesis 2

(1) Production of Nickel Hydroxide

A source material nickel hydroxide 2 was obtained in the same manner asin Synthesis 1 above, except that the air oxidation at 80 for 72 hourswas not performed. The source material nickel hydroxide 2 was a singlephase of β-nickel hydroxide in a powder X-ray diffraction, and itsaverage valence of manganese was estimated to be 2.04.

(2) Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

Then, after 200 g of the source material nickel hydroxide 2 wasintroduced into 1 L of a 7 mol/L sodium hydroxide aqueous solution, asufficient amount of a sodium hypochlorite aqueous solution (effectivechlorine concentration: 5 wt %) serving as an oxidizing agent was addedthereto, and the whole was stirred to convert the nickel hydroxide intonickel oxyhydroxide. The resulting particles were sufficiently washedwith water, followed by vacuum drying at 60° C. (24 hours), therebyproducing a nickel oxyhydroxide m2.

[3] Synthesis 3

(1) Production of Nickel Hydroxide

A source material nickel hydroxide 3 was obtained in the same manner asin Synthesis 1 above, except that the particles were stood still in theair at 20 for one month, instead of being subjected to the air oxidationat 80 for 72 hours. In a powder X-ray diffraction of the source materialnickel hydroxide 3, some peaks of manganese oxyhydroxide and manganesedioxide were observed, in addition to those of the β-type nickelhydroxide, so that it was inferred that unstable manganese species wereliberated outside the crystal of the nickel hydroxide, because of beingstood still for a long period of time. The average valence of manganesein the source material nickel hydroxide 3 was 3.47.

(2) Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

Then, after 200 g of the source material nickel hydroxide 3 wasintroduced into 1 L of a 7 mol/L sodium hydroxide aqueous solution, asufficient amount of a sodium hypochlorite aqueous solution (effectivechlorine concentration: 5 wt %) serving as an oxidizing agent was addedthereto, and the whole was stirred to convert the nickel hydroxide intonickel oxyhydroxide. At this time, red coloration of the reaction liquiddue to the oxidation or dissolution of the liberated manganese specieswas clearly observed. The resulting particles were sufficiently washedwith water, followed by vacuum drying at 60° C. (24 hours), therebyproducing a nickel oxyhydroxide n2.

[4] Synthesis 4

(1) Production of Nickel Hydroxide

A source material nickel hydroxide 4 was obtained in the same manner asin Synthesis 1 described above, except that a nickel (II) sulfateaqueous solution, a manganese (II) sulfate aqueous solution, a sodiumhydroxide aqueous solution and ammonia water having predeterminedconcentrations were supplied with pumps into a reaction vessel providedwith a stirring blade such that the pH in the reaction vessel wasconstant, without performing the bubbling with a nitrogen gas and theaddition of hydrazine into the reaction vessel. The source materialnickel hydroxide 4 was a single phase of β-type nickel hydroxide in apowder X-ray diffraction, and had an average valence of manganese of2.45, an average particle diameter of 14 μm, a tap density of 2.04 g/cm³and a BET specific surface area of 10.9 m²/g.

(2) Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

Then, after 200 g of the source material nickel hydroxide 4 wasintroduced into 1 L of a 7 mol/L sodium hydroxide aqueous solution, asufficient amount of a sodium hypochlorite aqueous solution (effectivechlorine concentration: 5 wt %) serving as an oxidizing agent was addedthereto, and the whole was stirred to convert the nickel hydroxide intonickel oxyhydroxide. Also at this time, red coloration of the reactionliquid due to the oxidation or dissolution of the manganese species wasclearly observed. From this, it was inferred that, in the sourcematerial nickel hydroxide 4, a majority of the manganese ions wereinserted in an unstable state in the crystal of the nickel hydroxide.The resulting particles were sufficiently washed with water, followed byvacuum drying at 60 (24 hours), thereby producing a nickel oxyhydroxideo2.

[5] Synthesis 5

(1) Production of Nickel Hydroxide

After a hydrogen peroxide solution was added to a manganese (II) sulfateaqueous solution, a sodium hydroxide aqueous solution was added theretoto adjust the pH, thus preparing a solution in which manganese ions werepresent in a trivalent state. This solution, a nickel (II) sulfateaqueous solution, a sodium hydroxide aqueous solution and ammonia waterwere supplied with pumps into a reaction vessel provided with a stirringblade such that the pH in the vessel was constant, and continuousstirring was performed sufficiently, thus precipitating and growingnickel hydroxide including a α-type crystal structure and containing 10mol % of trivalent Mn. The resulting particles were sufficiently washedwith water, followed by vacuum drying, thereby producing a sourcematerial nickel hydroxide 5. The source material nickel hydroxide 5 wasa single phase of α-nickel hydroxide in a powder X-ray diffraction, andhad an average valence of manganese of 3.02, an average particlediameter of 13 μm, a tap density of 1.28 g/cm³ and a BET specificsurface area of 24.5 m²/g.

(2) Oxidation of Nickel Hydroxide to Nickel Oxyhydroxide

Then, after 200 g of the source material nickel hydroxide 5 wasintroduced into 1 L of a 7 mol/L sodium hydroxide aqueous solution, asufficient amount of a sodium hypochlorite aqueous solution (effectivechlorine concentration: 5 wt %) serving as an oxidizing agent was addedthereto, and the whole was stirred to convert the nickel hydroxide intonickel oxyhydroxide. Also at this time, red coloration of the reactionliquid due to the oxidation or dissolution of the manganese species wasobserved. From this, it was inferred that, in the source material nickelhydroxide 5, a majority of the manganese ions were inserted in anunstable state in the crystal of the nickel hydroxide. The resultingparticles were sufficiently washed with water, followed by vacuum dryingat 60° C. (24 hours), thereby producing a nickel oxyhydroxide p2.

[6] Analysis of Physical Properties of Nickel Oxyhydroxides

Table 10 shows the values of I_(γ)/(I_(γ)+I_(β)), the contents ofnickel, the average valences of nickel, the tap densities, the contentsof water, the average particle diameters, the BET specific surface areasthat were obtained for the nickel oxyhydroxides g2 to p2. TABLE 12Average Powder X-ray Nickel Average Tap Water particle BET specific Typeof nickel diffraction content nickel density content diameter surfacearea oxyhydroxide I_(γ)/(I_(γ) + I_(β)) [wt %] valence [g/cm³] [wt %][μm] [m²/g] Nickel oxyhydroxide g2 0.06 54.2 3.08 2.15 0.45 14.3 10.2Nickel oxyhydroxide h2 0.24 54.0 3.15 2.13 0.84 15.0 11.0 Nickeloxyhydroxide i2 0.46 52.8 3.27 2.02 1.12 15.2 12.4 Nickel oxyhydroxidej2 0.72 52.1 3.39 1.91 1.55 14.6 15.3 Nickel oxyhydroxide k2 0.88 51.53.48 1.84 1.78 14.0 16.2 Nickel oxyhydroxide l2 0.97 51.0 3.55 1.73 1.8512.9 18.5 Nickel oxyhydroxide m2 0.89 51.4 3.48 1.65 1.82 13.0 20.3Nickel oxyhydroxide n2 0.86 51.4 3.45 1.59 1.84 13.3 22.5 Nickeloxyhydroxide o2 0.91 51.2 3.49 1.48 3.51 12.5 31.5 Nickel oxyhydroxidep2 0.95 48.9 3.54 1.25 3.65 13.1 33.8

It can be seen that, with an increase (from g2 to l2) in theconcentration of the sodium hydroxide aqueous solution that was presentduring the chemical oxidation of the source material nickel hydroxide 1,the value of I_(γ)/(I_(γ)+I_(β)) increased and the oxidation of nickelthus proceeded. The reason for this can be understood as follows:Increasing the concentration of the sodium hydroxide aqueous solutionallowed the alkali metal ions to be effectively inserted between theNiO₂ layers of the nickel oxyhydroxide to maintain the electricalneutrality of the quadrivalent nickel ions, thus accelerating thereaction for forming higher order nickel.

Further, it was confirmed that the nickel oxyhydroxides m2 to p2, whichwere obtained by a chemical oxidation treatment of the source materialnickel hydroxides 2 to 5, provided a powder X-ray diffraction patternsimilar in appearance to that of the nickel oxyhydroxide l2, which wasobtained from the source material nickel hydroxide 1, and also had asimilar average valence of nickel.

[7] Fabrication of Alkaline Batteries

Nickel-manganese batteries as shown in FIG. 1 were fabricated in thesame manner as in Example 5, except for using the nickel oxyhydroxidesg2 to p2, respectively, in place of the nickel oxyhydroxide a2 to f2.The batteries using the nickel oxyhydroxides g2 to p2 were namedbatteries G2 to P2, respectively.

[8] Evaluation of Alkaline Batteries

Each of the batteries A2 to F2 was continuously discharged at 20° C.with a constant current of 50 mA, and the discharge capacity obtainedduring a period in which the battery voltage reached an end voltage of0.9 V was measured. The results obtained were summarized in Table 13. Itshould be noted that, in Table 13, the values of the discharge capacitywere shown as relative values, taking the discharge capacity of thebattery A2 of Example 5 as 100. TABLE 13 Battery capacity Type of Typeof (standardized battery nickel oxyhydroxide value) Battery G2 Nickeloxyhydroxide g2 101 Battery H2 Nickel oxyhydroxide h2 102 Battery I2Nickel oxyhydroxide i2 102 Battery J2 Nickel oxyhydroxide j2 110 BatteryK2 Nickel oxyhydroxide k2 113 Battery L2 Nickel oxyhydroxide l2 116Battery M2 Nickel oxyhydroxide m2 106 Battery N2 Nickel oxyhydroxide n2106 Battery O2 Nickel oxyhydroxide o2 96 Battery P2 Nickel oxyhydroxidep2 92

The source material nickel hydroxide 1 was obtained by performing airoxidation on a solid solution β-nickel hydroxide in which Mn wasdissolved, which was obtained by reaction crystallization, and oxidizingonly Mn. On the other hand, the nickel oxyhydroxides j2 to l2 wereobtained by chemically oxidizing the source material nickel hydroxide 1with a sodium hypochlorite aqueous solution in a sodium hydroxideaqueous solution at 3 mol/l or more. The batteries J2 to L2, which usedthe nickel oxyhydroxides j2 to 12, provided a remarkably higher capacitythan the batteries using the nickel oxyhydroxides obtained by otherprocesses.

The reason that the capacities of the batteries J2 to L2 were remarkablyhigher than those of the batteries G2 to I2 can be explained similarlyas in Example 5. That is, the γ-NiOOH that was formed at a stage wherethe average valence of nickel was relatively small, such as the nickeloxyhydroxides g2 to i2, seems to have not made much contribution to thedischarge capacity. On the other hand, the γ-NiOOH that was formed at astage where the average valence of nickel was about not less than 3.3,such as the nickel oxyhydroxides j2 to l2, seems to have had highactivity, thus providing a large discharge capacity corresponding tothat valence.

The batteries M2 and N2 also exhibited a higher discharge capacityhigher than the batteries G2 to I2. The nickel oxyhydroxides of thebatteries M2 and N2 had physical properties that were substantiallyequivalent to those of the nickel oxyhydroxide 1, which was obtainedfrom the source material nickel hydroxide 1. Therefore, it seems thatthe batteries M2 and N2 had the most excellent discharge characteristicsafter those of the batteries J2 to K2.

The nickel hydroxide 2, which was the source material of the nickeloxyhydroxide m2 used for the battery M2, had not undergone the treatmentfor oxidizing Mn. Although the detailed mechanism is unknown, it isconsidered that when nickel hydroxide is treated with an oxidizing agentin a state in which Mn has not been oxidized into a higher oxidationstate, localized liberation or the like of the manganese oxide occurs inthe particles, for example, due to the movement of the manganese speciesin the crystal. However, such liberation of the manganese oxide isconsidered to be at a level that cannot be found by a commonly usedpowder X-ray diffraction method. Thus, it is inferred that, in thenickel oxyhydroxide m2, the amount of production of γ-nickeloxyhydroxide having high discharge efficiency that could contribute toan increase of the battery capacity was small. Likewise, it is inferredthat battery N2 was also affected by the liberated manganese.

Although the nickel oxyhydroxides o2 and p2, which were used for thebatteries O2 and P2, were similar to the nickel oxyhydroxide l2 (or k2)in the powder X-ray diffraction or the average valence of nickel, theyexhibited a smaller capacity. Since the phenomenon of liberation ofmanganese species and the dissolution of manganese, for example, wereconfirmed during production of the nickel oxyhydroxides o2 and p2, it isinferred that the discharge reaction of the nickel oxyhydroxide washindered by the manganese species. In particular, the nickeloxyhydroxide o2 and p2 had a water content exceeding 3 wt % and a BETspecific surface area exceeding 30 m²/g. Therefore, it seems that theelectrolyte distribution in the positive electrode material mixture, forexample, in the batteries O2 and P2 was significantly different fromthat in the rest of the batteries, and this affected the capacity.

EXAMPLE 7

[1] Production of Nickel Oxyhydroxide

Nickel oxyhydroxides r1 to r6 were prepared in the same manner as withthe nickel oxyhydroxide L2 of Example 6, except for varying the ratiobetween the nickel (II) sulfate aqueous solution and the manganese (II)sulfate aqueous solution, as well as the content of manganese in thesource material nickel hydroxide.

Further, nickel oxyhydroxides s1 to s6 were prepared in the same manneras with the nickel oxyhydroxide L2 of Example 6, except for varying theratio between the nickel (II) sulfate aqueous solution and the manganese(II) sulfate aqueous solution, as well as the content of manganese inthe source material nickel hydroxide, and reducing the amount of thesodium hypochlorite aqueous solution added in the chemical oxidation.

[2] Analysis of Physical Properties of Nickel Oxyhydroxides

Table 14 shows the values of I_(γ)/(I_(γ)+I_(β)), the contents ofnickel, and the average valences of nickel that were obtained for thenickel oxyhydroxides r1 to r6 and s1 to s6. TABLE 14 Powder AverageBattery X-ray Nickel valence capacity Type of diffraction content of(standardized nickel oxyhydroxide I_(γ)/(I_(γ) + I_(β)) [wt %] nickelvalue) Nickel oxyhydroxide r1 0.95 57.5 3.54 126 Nickel oxyhydroxide r20.94 54.2 5.53 122 Nickel oxyhydroxide r3 0.96 51.0 3.55 116 Nickeloxyhydroxide r4 0.95 48.1 3.52 110 Nickel oxyhydroxide r5 0.96 44.2 3.55104 Nickel oxyhydroxide r6 0.95 41.0 3.54 97 Nickel oxyhydroxide s1 0.5157.7 3.34 117 Nickel oxyhydroxide s2 0.52 54.3 3.32 114 Nickeloxyhydroxide s3 0.52 51.2 3.33 110 Nickel oxyhydroxide s4 0.51 48.4 3.32104 Nickel oxyhydroxide s5 0.50 44.6 3.31 99 Nickel oxyhydroxide s6 0.5141.3 3.34 92 Nickel oxyhydroxide a2 0.01 62.2 3.03 100[3] Fabrication of Alkaline Batteries

Nickel-manganese batteries as shown in FIG. 1 were fabricated in thesame manner as in Example 5, except for using the nickel oxyhydroxides r1 to r6 and s1 to s6, respectively, in place of the nickel oxyhydroxidesa2 to f2. The batteries using the nickel oxyhydroxides r1 to r6 werenamed batteries R1 to R6, respectively. Further, the batteries using thenickel oxyhydroxides s1 to s6 were named batteries S1 to S6,respectively.

[4] Evaluation of Alkaline Batteries

Each of the batteries R1 to R6 and S1 to S6 was continuously dischargedat 20° C. with a constant current of 50 mA, and the discharge capacityobtained during a period in which the battery voltage reached an endvoltage of 0.9 V was measured. The results obtained were summarized inTable 14. It should be noted that, in Table 13, the values of thedischarge capacity were shown as relative values, taking the dischargecapacity of the battery A2 of Example 5 as 100.

From Table 14, it can be seen that the use of nickel oxyhydroxideshaving a nickel content of not less than 45 wt % could achieve a highercapacity than the battery using the nickel oxyhydroxide a2, even whenthe value of I_(γ)/(I_(γ)+I_(β)) and the average valence of nickel wereabout 0.5 and about 3.3, respectively, which were not so large.

Although in the above-described examples the air oxidation was performedat 80° C. for 72 hours at the time of oxidizing manganese in the solidsolution nickel hydroxide in which Mn was dissolved, similar results canalso be obtained by increasing the valence of manganese to not less than3.5, more preferably not less than 3.8, by appropriately adjusting theoxidation time at 50 to 150° C. under ambient atmosphere.

Although in the above-described examples the treatment was performed ina sodium hydroxide aqueous solution at the time of chemically oxidizingnickel with sodium hypochlorite, similar results can also be obtained byusing a potassium hydroxide aqueous solution, a lithium hydroxideaqueous solution, or a mixed alkaline aqueous solution of these.

Although in the above-described examples 5 wt % of zinc oxide was addedto the nickel oxyhydroxide in the positive electrode material mixture,this is not essential feature of the present invention.

Although in the above-described examples so-called inside-out typenickel-manganese batteries were fabricated, in which a positiveelectrode material mixture pellet in the form of a short cylinder, aseparator and a gelled zinc negative electrode were disposed in acylindrical positive electrode case. However, the present invention canalso be adapted to alkaline batteries in other structures, includingthose of the button type and the square type.

INDUSTRIAL APPLICABILITY

While the present invention is applicable to various types of alkalinebatteries, it is particularly useful for nickel-manganese batteries.Furthermore, since the present invention can realize a significantcapacity increase for alkaline batteries without impairing the heavyload discharge characteristics, it is particularly useful for alkalinebatteries serving as the power sources for devices requiring high loadpower.

1. An alkaline battery comprising a positive electrode material mixture, a negative electrode, a separator interposed between said positive electrode material mixture and said negative electrode, and an alkaline electrolyte, wherein said positive electrode material mixture includes a first active material comprising nickel oxyhydroxide and a second active material comprising manganese dioxide, said nickel oxyhydroxide includes a γ-type crystal structure, the content of nickel in said nickel oxyhydroxide is not less than 45 wt %, and the average particle diameter on a volume basis of said nickel oxyhydroxide measured with a laser diffraction particle size distribution analyzer is 3 to 20 μm.
 2. The alkaline battery in accordance with claim 1, wherein said nickel oxyhydroxide further includes a β-type crystal structure.
 3. The alkaline battery in accordance with claim 1, wherein the tap density of said nickel oxyhydroxide after 500 times of tapping is not less than 1.5 g/cm³, the content of water in said nickel oxyhydroxide is not more than 3 wt %, and the specific surface area of said nickel oxyhydroxide measured by a BET method is 10 to 30 m²/g.
 4. The alkaline battery in accordance with claim 1, wherein a powder X-ray diffraction pattern of said nickel oxyhydroxide includes a diffraction peak P_(γ) attributed to the (003) plane of a γ-type crystal having an interplanar spacing of 6.8 to 7.1 angstroms (Å) and a diffraction peak P_(β) attributed to the (001) plane of a β-type crystal having an interplanar spacing of 4.5 to 5 angstroms (Å), an integrated intensity I_(γ) of said diffraction peak P_(γ) and an integrated intensity I_(β) of said diffraction peak P_(β) satisfy 0.5≦I_(γ)/(I_(γ)+I_(β)), and the average valence of nickel included in said nickel oxyhydroxide is not less than 3.3.
 5. The alkaline battery in accordance with claim 1, wherein a powder X-ray diffraction pattern of said nickel oxyhydroxide includes a diffraction peak P_(γ) attributed to the (003) plane of a γ-type crystal having an interplanar spacing of 6.8 to 7.1 angstroms (Å) and a diffraction peak P_(β) attributed to the (001) plane of a β-type crystal having an interplanar spacing of 4.5 to 5 angstroms (Å), an integrated intensity I_(γ) of said diffraction peak P_(γ) and an integrated intensity I_(β) of said diffraction peak P_(β) satisfy 0.1≦I_(γ)/(I_(γ)+I_(β))<0.5, and the average valence of nickel included in said nickel oxyhydroxide is not less than 3.05 and less than 3.3.
 6. The alkaline battery in accordance with claim 1, wherein said nickel oxyhydroxide is a solid solution in which an additive element is dissolved, and said additive element is at least one selected from the group consisting of manganese and cobalt.
 7. The alkaline battery in accordance with claim 6, wherein said nickel oxyhydroxide is a solid solution in which manganese is dissolved as said additive element, and the amount of manganese dissolved in said solid solution is 1 to 7 mol % of the total of all the metallic elements included in said solid solution.
 8. The alkaline battery in accordance with claim 6, wherein said nickel oxyhydroxide is a solid solution in which both manganese and cobalt are dissolved as said additive element, and the amount of each of manganese and cobalt dissolved in said solid solution is 1 to 7 mol % of the total of all the metallic elements included in said solid solution.
 9. The alkaline battery in accordance with claim 1, wherein said nickel oxyhydroxide is a solid solution in which manganese is dissolved as an additive element, and said solid solution carries a cobalt oxide attached onto a surface thereof.
 10. The alkaline battery in accordance with claim 9, wherein the amount of manganese dissolved in said solid solution is 1 to 7 mol % of the total of all the metallic elements included in said solid solution, and the amount of said cobalt oxide is 0.1 to 7 wt % of said solid solution.
 11. The alkaline battery in accordance with claim 9, wherein the average valence of cobalt included in said cobalt oxide is greater than 3.0.
 12. The alkaline battery in accordance with claim 1, wherein the content of said manganese dioxide in said positive electrode material mixture is 20 to 90 wt %.
 13. A method for producing a positive electrode material for an alkaline battery, said method comprising: a fist step of performing an operation of supplying a nickel (II) sulfate aqueous solution, a manganese (II) sulfate aqueous solution, a sodium hydroxide aqueous solution and ammonia water into a reaction vessel provided with a stirring blade through separate channels, while bubbling an inert gas and adjusting the temperature and pH in said reaction vessel, thereby obtaining nickel hydroxide including a β-type crystal structure in which nickel sites are partly replaced with divalent manganese; a second step of washing with water and drying said nickel hydroxide that has been obtained by said first step, followed by heating at 50 to 150% under an oxidizing atmosphere, thereby oxidizing manganese to an average valence of not less than 3.5; and a third step of introducing said nickel hydroxide that has been subjected to said second step into an alkaline aqueous solution, together with an oxidizing agent, thereby chemically oxidizing said nickel hydroxide.
 14. The method for producing a positive electrode material for an alkaline battery in accordance with claim 13, wherein, in said first step, hydrazine is further added into said reaction vessel to maintain a reducing atmosphere.
 15. The method for producing a positive electrode material for an alkaline battery in accordance with claim 13, wherein, in said second step, said average valence of manganese is set to not less than 3.8.
 16. The method for producing a positive electrode material for an alkaline battery in accordance with claim 13, wherein said oxidizing agent used in said third step is hypochlorite.
 17. The method for producing a positive electrode material for an alkaline battery in accordance with claim 13, wherein said alkaline aqueous solution used in said third step is an aqueous solution in which at least one alkali salt selected from the group consisting of potassium hydroxide, sodium hydroxide and lithium hydroxide is dissolved.
 18. The method for producing a positive electrode material for an alkaline battery in accordance with claim 17, wherein the concentration of said alkali salt in said alkaline aqueous solution is not less than 3 mol/L. 